Toxn

Mini-competition suggestions, for consideration some time next year:
 
1. Design an AT gun (2239)
 
In this mini-competition, contestants would be asked to design a conventional, WW2-era AT gun for use by one of the post-apocalyptic US polities. The gun would be designed with an understanding of how weapon and armour technology would be likely to develop, and should include a description of the gun itself, its mounting and its ammunition.
 
2. Design a ATGM (2247)
 
In this mini-competition, contestants would be asked to design an ATGM for use by the Texans, in a project running parallel to their first forays into MBT building. The contestants would have to simulate the overall configuration and aerodynamics of the ATGMs using OpenRocket, and would have to provide a coherent explanation for the warhead layout and control scheme. Submissions would be in the form of ORK files and a brief description.
 
3. "Fix a tank" 2 - France, 1946
 
The second "fix a tank" competition, this time to try and fix the problems that the French had with their post-war Panthers. The contestants would not be allowed to radically re-design the vehicles (or, at least, would have to provide better and better justifications for each new change), but would try to work with what they had to fix as many issues as possible. The goal would be to produce a vehicle that the historical 501st and 503rd armoured regiments could operate into the 1950s.
 
4. "Fill in the blanks" - design the Californian heavy from the first (2239) competition
 
The Californian heavy tank (which was very obviously an expy of the WW2-era Tiger) was the vehicle which kicked off the entire arms race that has become the dominant narrative of the post-apocalyptic competitions. A cryptic beast, it was described as weighing 50mt, having 76mm of armour and being armed with an 89mm gun that can penetrate ~140mm of RHA at 1000m.
 
This competition would involve contestants filling in the blanks to create a tank that fits these criteria (ie: not inventing a vehicle with a better gun, massively thick armour etc). The submissions would be done using a formula approach (for which, see here) with the contestants being asked only to model the hull/turret armour layout in detail (ie: in terms of mass). Everything else (the gun, ammunition, suspension, engine, optics etc.) can be simply a visual representation with standard weights being applied for variable-weight components. The submission would be in the form of drawings (front, side, top view) and a description to follow a standard format.

Main Battle Tank, 2247, project names "Derebus" and "Derebus-M"
 
 



Manufacturer: Manufactuer: Paramount-Allen-Fullerton (Para-allful) Conglomerated
 
Table of basic statistics:
 
Note: all statistics provided are for Derebus unless otherwise noted.
 
Parameter
Value
Mass, combat
Armour mass: (1-2" (25-50mm) RHA base plus ERA, composites, side skirts and engine bay liner): 20.6t (18.5mt)
 
43.1t (39.1mt) modelled, 43.4t (39.4mt) calculated
Length, combat (transport)
246" (6.25m) hull, 379" (9.63m) total 
Width, combat (transport)
150" (3.8m) with skirt
Height, combat (transport)
95" (2.41m) to top of commander's hatch, 109" (2.77m) total
Ground Pressure, zero penetration
Ground pressure (calculated MMP): 29.4 PSI (203 KPa). 
 
Nominal ground pressure (based on calculated weight): 10.3 PSI (70.77 KPa)
Estimated Speed
37 mph (60km/h)
Estimated range
490 mi at 30 mph
Crew, number (roles)
4 (commander, gunner, loader, driver)
Main armament, caliber (ammo count ready/stowed)
5-inch 55 calibre (127mm L/55) high/low pressure gun, (19 charges, 9 active projectiles, 10 inert projectiles in turret/ 16 charges, 8 active projectiles, 8 inert projectiles in hull)
Secondary armament, caliber (ammo count ready/stowed)
3 x .30 cal MG (600 rnd belted each ready/ 1200 rnd belted each stowed)
 
Vehicle designer’s notes:
 
The Derebus family of vehicles (provisionally named Derebus and Derebus-M) are intended to fulfil a procurement strategy emphasizing mobility (tactical, operational and strategic), reliability and superb value for money, achieved using a lightweight vehicle design, proven automotive components and a high/low capability mix. Derebus sports a state-of-the-art fire control system allied to a powerful 5" gun, while Derebus-M provides supporting firepower and a larger ammunition load thanks to it's 4" gun. Both vehicles provide superb protection across their frontal arcs, with the Derebus making use of cutting-edge composites to save weight. Both Derebus and Derebus M are immediately available to fulfil all of your defense needs.
 
Vehicle feature list:

Mobility:
 
1.     Link to Appendix 1
2.     Engine- V-12 Diesel (Kharkiv V-2-55 derivative), 2441 ci (40l) displacement, 600HP (448kW), liquid-cooled. 
 
Note: alternate engine and transmission arrangements are provided for in Appendix 3
 
3.     Transmission - hydraulic torque converter feeding into Merritt-Brown-style double differential system, 7 forward/1 reverse gears.
4.     Fuel - diesel, ~2400lb total (639lb/290kg in tanks flanking the driver, 1764lb/800kg in rear sponson tanks, estimated range of 490mi at 30mph.
5.     Engine, transmission and cooling are arranged in removable aluminium tub housed in engine bay. The tub is removable by sliding out the rear of the bay.
6.     Suspension - torsion bar, variable travel (presently 11.8" (30cm)), 20" (0.5m) ground clearance, geared torsion bar suspension, each axle pair in detachable units shrouded by aluminium housings. Wheels are 23.6" (0.6m) in diameter, with a track width of 27.6" (0.7m) and a pitch of 7.7" (0.195m).
 
Survivability:
 
1.     Link to Appendix 1
2.     Link to Appendix 2
3.     Non-specified survivability features and other neat tricks - highly sloped turret and hull front (75 degrees), charges and active ammunition (HEAT-FS and HE) arranged in sealed tubes leading to a blast chimney that outlets to blow-off panels in the turret roof, turret sides, hull roof and hull sides.
 
A.    Weapons:
 
1.     Link to Appendix 1
 
2.     Main Weapon-
 
a.      Type: smoothbore, vertically trainable +15/-10 degrees
 
b.      Caliber: 5"/127mm
 
c.      ammunition types and performance:
 
Note: the armour used for the target has the same hardness (360BRN) as the armour used in the vehicle. The target was at 0 degree obliquity for calculation purposes.
HEAT-FS (low-pressure setting): 46lb (20.85kg), penetration of around 21" (535mm), 3074fps (937m/s). HE (low-pressure setting): 46lb (23.2kg), 201oz (5.7kg) fill, estimated blast penetration of ~55mm RHA, 2910fps (887m/s) APFSDS (high-pressure setting): 15:1 LD, 550BHN monosteel body, tungsten insert, 115mm cap, ring sabot, 1800m/s, 15.7/13.8" (400/350mm) penetration at 100/2000y (lower estimate, 17.1" (435mm) at 2000y upper estimate). d.     Ammo stowage arrangement - 19 charges, 9 active projectiles, 10 inert projectiles in turret; 16 charges, 8 active projectiles, 8 inert projectiles in hull.
 
e.      FCS:
Duel axis stabilized main gun Semi-autoloader: the loader places the charge and warhead on trays in the bustle. these are then fed into the gun using an automatic mechanism (horizontal rammer, pivoting loading tray and rigid chain actuator to ram the warhead and charge home). The gun automatically returns to the loading position after each shot. A short spring at the end of the actuator helps to smooth out the loading impulse.  
f.      Neat features: 
Gun has a high-pressure and low-pressure recoil option, selectable on the slide – this doesn’t affect the recoil mechanism, it just changes where the trip key is to unlock the breech (warning: don’t fire high-pressure ammo with the low-pressure setting selected!) Gun uses a separate 6.9x27" (175x685mm) charge: 44lb/20kg mass, semi-combustible case built along the lines of the 4Zh-40 charge used with the historical 125mm 2A26 gun), matching the length of the HEAT-FS round. The charge gives space to produce a more powerful round to match higher future barrel higher pressures (when using a secondary charge with the APFSDS projectile itself). 74000 PSI (510 MPa) gives a potential power of 15MJ. 94000PSI (650 MPa) gives a potential power of 19MJ. Final penetration potential of the gun with early monobloc DU projectiles is something in the region of 22" (550mm) at 2000y (putting it on par with Mango and Vant). Being able to store and handle a longer projectile (ie: above 27") would probably allow something a bit better than Snivets.  Low-pressure charges are shortened (17.1" / 435mm) and come with an ejection spring to work with the same storage tubes as the high-pressure charges. 3.     Secondary weapons - 3 x .30 cal MG, 1 coaxial, 2 in mountings attached to the commander and loader's turret hatch
 
4.     Link to Appendix 3. 
 
B.    Optics:
 
1.     Primary gunsight: single axis stabilized gunner’s sight
 
2.     Secondary gunsight: vertical coincidence rangefinder (stadiametric, 39.4" (1m) base), doubles as a redundant back-up sight.
 
3.     Miscellaneous optics:
Commander and loader's rotating hatches, including vertically trainable (+/- 15 degrees) periscope in front of hatch, degree markings on hatch ring to allow rough direction of gunner to target. Driver's periscope, vertically trainable +/- 15 degrees  
C.    FCS:
 
1.     List of component systems, their purpose and the basic system architecture:
Simple electronic gun-follows sight fire control system (encoder connected to sight mirror feeds elevation data into a transistor-based PID controller, which tries to match position on a similar encoder connected to the gun. When gun position and sight position align, the firing mechanism is electronically triggered). LRF mounted above barrel, solid-state components, maximum operating range of 5km in clear conditions, average estimation error of 1%. Uses flashlamp-pumped ruby laser, optical sensor, quartz timing circuit and the sequential event time sampling approach (with post-sampling amplification) to allow time-of-flight rangefinding using a lower timebase and bandwidth compatible with current electronics.  
2.     Link to Appendix 3.
 
Fightability:
 
1.     List vehicle features which improve its fightability and useability:
 
Engine bay approach simplifies engine and transmission replacement via rear bay doors. Generous rear hull roof hatches simplify servicing and maintenance. Bolt-on suspension units simplify field replacement and repair. Commander and loader's hatch design improves buttoned-up visibility   
Additonal Features:
 
See Appendix 3  
Free expression zone: 
 
"...bellicis"

Good going!
We'll look forward to your entry.

Promo shot from the recent ergonomics testing.

Still chipping away at the Brahman, just about ready to start modeling the armor. 

 
If you're wondering how I'm going to protect the inlet and outlet to the engine, I'm going to use the same trick I used in the californium competition to protect the holes in the side, but slightly thicker. 
 
The plate above the engine is the radiator, which additionally has a 2 inch gap above and below it, where air is forced across it, to cool it. The exhaust and coolant air are both passed through the turbo charger, then through a CV90 type system, to cool it down and hopefully reducing the thermal signature. 
 
I'm going to access the engine and transmission via a similar system to the Merkava 4: the upper plate lifts up, using 2 hydraulic pistons powered by the tanks batteries; or if you need to pull the engine and tranny, you can lift off the upper plate with the same 5+ ton crane you need to lift the drive train. 
 
 
I need a little help, I don't know how to model a "modern" commanders cupola, with all the amenities, without making it too damn big. 

Comanche is close to being finished:


 
62.6 s.tons so far.

Final Entry: Main Battle Tank, 2247, project name "Derebus"
 

 
Main dimensions and statistics
Manufacturer: Paramount-Allen-Fullerton (Para-allful) Conglomerated Mass estimate (as based on CAD model plus ~6600lb to account for drive systems, crew amenities, ammunition and miscellaneous components): 43.1t (39.1mt) fully loaded, fueled. Armour mass (1-2" (25-50mm) RHA base plus ERA, composites, side skirts and engine bay liner): 20.6t (18.5mt) Calculated mass: 43.4t (39.4mt) Crew: 4 (commander, gunner, loader, driver) Length: 246" (6.25m) hull, 379" (9.63m) total  Width:  150" (3.8m) with skirt Height: 95" (2.41m) to top of commander's hatch, 109" (2.77m) total  

Firepower

Note: the armour used for the target has the same hardness (360BRN) as the armour used in the vehicle. The target was at 0 degree obliquity for calculation purposes.
 
Main gun: 5-inch 55 calibre (127mm L/55) high/low pressure gun “High pressure” = 70000 PSI (480 MPa) operating pressure, 14.16MJ energy. Vertical travel: +15'/-10'  
Ammunition:
46lb (20.85kg) HEAT-FS, penetration of around 21" (535mm) using 122mm BK13 derivative (420mm if using BK13 penetration), 3074fps (937m/s), 9.14MJ using a low-pressure charge (~45k PSI). 46lb (23.2kg) HE, (5.7kg) fill, estimated blast penetration of ~55mm RHA, 2910fps (887m/s) Simple APFSDS (15:1 LD, 550BHN monosteel body, tungsten insert, 115mm cap, ring sabot): 1.57x23.54" (40x597mm) rod, 0.866x5.24" (22x133mm) insert, 14.2/5.2lb (5.6/3.2kg) penetrator/sabot mass, 1800m/s, 15.7/13.8" (400/350mm) penetration at 100/2000y.  
Note: if following the design of 3BM-26, this could be higher in practice. Using DeMarre the estimated penetration is 17.1" (435mm) at 2000y. Upgraded monobloc projectiles could match and eventually improve on this, up to 25.6" (650mm) before needing to rework the ammunition storage.
 
Details:
 
Gun has a high-pressure and low-pressure recoil option, selectable on the slide – this doesn’t affect the recoil mechanism, it just changes where the trip key is to unlock the breech. Warning: don’t fire high-pressure ammo with the low-pressure setting selected! Gun uses a separate 6.9x27" (175x685mm) charge: 44lb/20kg mass, semi-combustible case built along the lines of the 4Zh-40 charge used with the 2A26 gun), matching the length of the HEAT-FS round. This charge gives space to produce a more powerful round to match higher future barrel higher pressures (when using a secondary charge with the APFSDS projectile itself). 74000 PSI (510 MPa) gives a potential power of 15MJ. 94000PSI (650 MPa) gives a potential power of 19MJ. Final penetration potential of the gun with early monobloc DU projectiles is something in the region of 22" (550mm) at 2000y (putting it on par with Mango and Vant). Being able to store and handle a longer projectile (ie: above 27") would probably allow something a bit better than Snivets.  Low-pressure charges are shortened (17.1" / 435mm) and come with an ejection spring to work with the same tubes as the high-pressure charges.  
Storage:
19 charges and 9 active projectiles (HE and HEAT) in armoured tubes in the turret. The tubes are sealed at the front and lead to a blast chimney that outlets to blow-off panels in the turret roof. 10 inert projectiles (APFSDS) are stored in various places in the turret space, held by retaining clips. 16 charges and 8 active projectiles are stored on either side of the driver behind the fuel cells, also using the blast chimney approach (exhausting out the hull sides). 8 inert projectiles are stored in various spots in the hull.  
Secondary weapons: 
.30cal MG as coax Both the commander and loader’s hatch rotate and have mounts for .30 cal MGs.  
Fire control:
Single axis stabilized gunner’s sight Duel axis stabilized main gun Vertical coincidence rangefinder (stadiametric, 39.4" (1m) base) which doubles as a redundant back-up sight. Simple electronic gun-follows sight fire control system (encoder connected to sight mirror feeds elevation data into a transistor-based PID controller, which tries to match position on a similar encoder connected to the gun. When gun position and sight position align, the firing mechanism is electronically triggered). Semi-autoloader: the loader places the charge and warhead on trays in the bustle. these are then fed into the gun using an automatic mechanism (horizontal rammer, pivoting loading tray and rigid chain actuator to ram the warhead and charge home). The gun automatically returns to the loading position after each shot. A short spring at the end of the actuator helps to smooth out the loading impulse. LRF mounted above barrel.  
Note: Industrial espionage has allowed Texan engineers to copy the laser rangefinder proposed for use in the Cascadian M8A1 upgrade package. The Texan copy of the LRS-2 ruby laser rangefinder uses a flashlamp-pumped ruby laser, optical sensor, quartz timing circuit and the sequential event time sampling approach (with post-sampling amplification) to allow time-of-flight rangefinding using a lower timebase and bandwidth compatible with current electronics. Solid state electronic components allow the system to be fairly compact and robust. The rangefinder features a numerical readout in the gunner’s station. The rangefinder has a maximum operating range of 5km in clear conditions and has an average estimation error of 1%. 
 
The TBC-3A ballistic computer and IAPO-3 sight were not copied, as the high velocity of the APFSDS used in the 5”/55 cal main gun was felt to provide sufficient accuracy when paired with a good rangefinder.
 
Mobility

Transverse-mounted Kharkiv V-2-derived engine (specifically the V-55 diesel): 600HP/448kW, 2248lb/1020kg dry weight. The engine has been slightly re-bored to 40l, but is otherwise mechanically very similar to the engine used on the historical T-62. Hydraulic torque converter feeding into Merritt-Brown-style double differential system. An alternate engine layout would be two V-6 engines of similar total displacement, mounted normally, with a combined linkage to the torque converter. The engine, transmission and cooling system all sit in an aluminium tub that fits into a bay in the rear of the vehicle. This can be removed entirely for servicing, or to replace the powerpack with a different configuration. Suspension: 20" (0.5m) ground clearance, geared torsion bar suspension, each axle pair in detachable units shrouded by aluminium housings. Wheels are 23.6" (0.6m) in diameter, with a track width of 27.6" (0.7m) and a pitch of 7.7" (0.195m). Fuel load: ~2400lb total (639lb/290kg in tanks flanking the driver, 1764lb/800kg in rear sponson tanks, range of 490mi at 30mph PWR: 13.8 HP/t (11.4 kW/mt) Ground pressure (calculated MMP): 29.4 PSI (203 KPa).  Track contact length: 153.5" (3.9m) Track contact area: 58.8ft2 (5.46m2) Nominal ground pressure (based on calculated weight): 10.3 PSI (70.77 KPa)  
Protection


Notes:
Composite liner (50:50 HHA/textolite): density of 4.825g/cm3, layers of 0.2, 0.4, 0.6, 0.8 or 1" depending, with thickness adjusted to prefer the thickest possible layers (1"/1") with a thinner backing layer. Mounting bolts for ERA layers are not modelled, but are accounted for. The covers over the rear fuel cells are 1" RHA.  
Turret front:
Two layers of L-ERA, sloped at 75’ Base armour: 1" (25mm) RHA sloped at 75’ 2.1" (55mm) composite (25mm HHA, 25mm textolite), sloped at 75’ KE: 16.9" (430mm) CE: 89" (2250mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/11.4" (455/290mm), corresponding to 3"/3" high/low-precision charges and a 4" form factor.  
Turret cheeks:
 
Note: because of how the cheeks are sloped, protection actually drops off the closer you get to the 25’ arc.
 
Three layers of L-ERA sloped at 25’ in the horizontal Base armour: 1" (25mm RHA), sloped at 25’ in the horizontal 2.2" (55mm) composite, sloped at 25’ in the horizontal KE: 11.4" (290mm) from the front CE: 55" (1400mm) (normal) vs single charge. Tandem charge rated to penetrate both layers via precursor is something like 12.2/7.3" (310/185mm), corresponding to 2.1/2.4" (55/60mm) high/low-precision charges and a 3" form factor.  
Turret side armour array:
Two layers of L-ERA sloped at ~30’ in the horizontal Base armour: 1" (25mm) RHA, sloped at ~30’ in the horizontal 1" (25mm) composite, sloped at 30’ in the horizontal KE: 5.9" (150mm) at 30’ from side. CE: 13.4" (340mm) at 30' from side. Maximum angle that side can resist 7" CE is ~20' from the side (70' from the front).  
 
Turret rear:
2" (50mm) RHA  
Turret roof:
1" (25mm) RHA  
Hull upper front:
Two layers of L-ERA, sloped at 75’ Base armour: 1" (25mm) RHA sloped at 75’ 2.2" (55mm) composite, sloped at 75’ KE: 16.9" (430mm) CE: 89" (2250mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/11.4" (455/290mm), corresponding to 3" high/low-precision charges and a 4" form factor.  
Hull lower front:
Base armour: 1" (25mm) RHA sloped at 45’ from vertical 4.2" (106mm) composite, sloped at 45’ from vertical KE: 7.3" (185mm) CE: 7.5" (190mm) vs single-charge. Notes: the area next to the driver contains two fuel cells and two protected storage areas for ammunition. Hits here are correspondingly much more protected than the above would indicate, for both the upper and lower hull.
 
Hull side:
2 x L-ERA layers Composite skirt: 0.2" (5mm) HHA with a 0.8" (20mm) textolite backing 1" (25mm) aluminium roadwheel (depending on hit location) 29.5" (750mm) air gap/fuel (depending on hit location) Inner skin: 1" (25mm) RHA KE: ~3" (75-80mm) (normal) / ~8.2" (190-225mm) (30’ arc from the front) CE: ~3.8" (95-100mm) (normal) / ~30" (690-860) (30’ arc from the front) Immunity zone against 15.7" KE: 21’ arc from front Immunity zone against 7" CE: 54’ from front (36' from the side)  
Notes: the upper hull side has numerous armoured brackets to hold the skirt. These would be expected to be hit when the impact is from the 30' arc, which would significantly improve protection.
 
Belly:
1" 25mm RHA 0-0.8" aluminium  
Notes: the suspension units are aluminium boxes, the torsion bars are modelled as 2.75" (70mm) bars and each swing arm is attached to a hollow steel tube. The mine protection for the floor of the vehicle is accordingly expected to be much higher than these figures would indicate.

Final entry: Derebus-M
 

 
Main dimensions and statistics
 
Manufacturer: Paramount-Allen-Fullerton (Para-allful) Conglomerated
Mass estimate (as based on CAD model plus ~5830lb to account for drive systems, crew amenities, ammunition and miscellaneous components): 40.5t (36.8mt) fully loaded, fueled.
Armour mass (1-3.15" (25-80mm) RHA base plus ERA, composites, side skirts and engine bay liner): 21.5t (19.5mt)
Calculated mass: 41.9t (38mt)
Crew: 4 (commander, gunner, loader, driver)
Length: 246" (6.25m) hull, 261" (6.62m) total 
Width:  150" (3.8m) with skirt
Height: 86" (2.19m) to top of commander's hatch, 91" (2.30m) total
 

 
Firepower
 
Note: the armour used for the target has the same hardness (360BRN) as the armour used in the vehicle. The target was at 0 degree obliquity for calculation purposes.
 
Main gun: 102mm L/40 “4-inch 40 calibre” low-pressure gun:
“Low-pressure” = 310 MPa/3.45MJ
“Emergency” pressure = 345MPa/3.83MJ
Recoil stroke: 300mm
Vertical travel: +20/-10’
 
Ammunition:
23.9lb (10.85kg) HEAT-FS, penetration of around 16.9" (430mm) using 122mm BK13 derivative (337mm if using BK13 penetration), 2614fps (797m/s). 26.2lb (11.90kg) HE, 2.92kg fill, estimated blast penetration of ~1.4" (35mm) RHA, 2496fps (761m/s). Simple APFSDS (15:1 LD, 550BHN monosteel body, tungsten insert, 76mm cap, ring sabot): 1x15.2" (26x387mm) rod, 0.55/3.4" (14x86mm) insert, 3.4/1.9lb (1.53/0.84kg) penetrator/sabot mass, 1800m/s, 10.3/9"(261/228mm) penetration at 100/2000y. Uses emergency pressure.  
Case: 4x19.7" (102x500mm) steel case, 4.7" (120mm base), OAL (HEAT-FS) = ~28" (700mm) Charge weight: 4.9lb (~2.2kg) standard, 5.4lb (2.46kg) emergency Case weight: 11.5lb (5.2kg) Overall weight (HEAT-FS): 40lb (18.25kg)  
Note: if following the design of 3BM-26, this could be higher in practice. Using DeMarre the estimated penetration is 10.8" (274mm) at 2000y.
 
Storage:
21 rounds stored in an armoured storage bin in the turret. The bin exhausts through blow-off panels in the turret side and roof.
36 rounds stored in armoured bins on either side of the driver behind the fuel cells, with blow-off panels in the hull side and front
 
Secondary weapons: 
.30cal/7.62mm MG as coax
Both the commander and loader’s hatch rotate and have mounts for .30 cal MGs.
 
Fire control:
Single axis stabilized gunner’s sight (of the same configuration as Derebus).
Backup 60mm telescopic sight mounted to mantlet.
Duel axis stabilized main gun.
LRF (of the same configuration as Derebus) mounted above barrel.
 

 
Mobility
 
2xV6 liquid-cooled diesels, 19l displacement each: 290hp/ 216kW each, 553kg dry weight each.
Combined output to hydraulic torque converter, feeding into Merritt-Brown-style double differential system.
The engine, transmission and cooling system all sit in an aluminium tub that fits into a bay in the rear of the vehicle. This can be removed entirely for servicing, or to replace the powerpack with a different configuration.
Suspension: 20" (0.5m) ground clearance, geared torsion bar suspension, each axle pair in detachable units shrouded by aluminium housings. Wheels are 23.6" (0.6m) in diameter, with a track width of 27.6" (0.7m) and a pitch of 7.7" (0.195m).
PWR: 13.8 HP/t (11.4 kW/mt)
Fuel load: ~2550lb total (793lb/360kg in tanks flanking the driver, 1764lb/800kg in rear sponson tanks, range of 540mi at 30mph
Ground pressure (calculated MMP): 28.4 PSI (196 KPa). 
Track contact length: 153.5” (3.9m)
Track contact area: 58.8ft2 (5.46m2)
Nominal ground pressure (using calculated mass): 9.86 PSI (68KPa)
 


 
Protection
 
 
Notes:
Mounting bolts for ERA layers are not modelled, but are accounted for.
The covers over the rear fuel cells are 1" RHA.
 
Turret front:
Two layers of L-ERA, sloped at 75’
Base armour: 3.15" (80mm) RHA sloped at 75’
KE: 18.3" (465mm)
CE: 104" (2650mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/12" (455/305mm), corresponding to 3"/3" high/low-precision charges and a 4" form factor.
 
Turret cheeks:
 
Note: because of how the cheeks are sloped, protection actually drops off the closer you get to the 25’ arc.
 
Three layers of L-ERA sloped at 25’ in the horizontal
Base armour: 3.15" (80mm RHA), sloped at 25’ in the horizontal
KE: 12" (305mm) from the front
CE: 56" (1425mm) (normal) vs single charge. Tandem charge rated to penetrate both layers via precursor is something like 12.2/7.3" (310/185mm), corresponding to 2.1/2.4" (55/60mm) high/low-precision charges and a 3" form factor.
 
Turret side armour array:
Two layers of L-ERA sloped at ~30’ in the horizontal
Base armour: 1" (25mm) RHA, sloped at ~30’ in the horizontal
KE: 5.9" (105mm) at 30’ from side.
CE: 13.4" (215mm) at 30' from side. Maximum angle that side can resist 7" CE is ~58' from the side (32' from the front).
 
 
Turret rear:
1.38" (35mm) RHA
 
Turret roof:
1" (25mm) RHA
 
Hull upper front:
Two layers of L-ERA, sloped at 75’
Base armour: 3.15" (80mm) RHA sloped at 75’
KE: 18.3" (465mm)
CE: 104" (2650mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/12" (455/305mm), corresponding to 3"/3" high/low-precision charges and a 4" form factor.
 
Hull lower front:
Base armour: 5.15" (131mm) RHA sloped at 45’ from vertical
KE: 7.3" (185mm)
CE: 7.3" (185mm) vs single-charge.
Notes: the area next to the driver contains two fuel cells and two protected storage areas for ammunition. Hits here are correspondingly much more protected than the above would indicate, for both the upper and lower hull.
 
Hull side:
2 x L-ERA layers
25mm RHA skirt
1" (25mm) aluminium roadwheel (depending on hit location)
29.5" (750mm) air gap/fuel (depending on hit location)
Inner skin: 1" (25mm) RHA
KE: ~3.5" (85-95mm) (normal) / ~9" (210-245mm) (30’ arc from the front)
CE: ~4.2" (100-115mm) (normal) / ~32" (730-890) (30’ arc from the front)
Immunity zone against 15.7" KE: 21’ arc from front
Immunity zone against 7" CE: 56’ from front (34' from the side)
 
Notes: the upper hull side has numerous armoured brackets to hold the skirt. These would be expected to be hit when the impact is from the 30' arc, which would significantly improve protection.
 
Belly:
1" 25mm RHA
0-0.8" aluminium
 
Notes: the suspension units are aluminium boxes, the torsion bars are modelled as 2.75" (70mm) bars and each swing arm is attached to a hollow steel tube. The mine protection for the floor of the vehicle is accordingly expected to be much higher than these figures would indicate.
 


 

Final entry: Derebus-M
 

 
Main dimensions and statistics
 
Manufacturer: Paramount-Allen-Fullerton (Para-allful) Conglomerated
Mass estimate (as based on CAD model plus ~5830lb to account for drive systems, crew amenities, ammunition and miscellaneous components): 40.5t (36.8mt) fully loaded, fueled.
Armour mass (1-3.15" (25-80mm) RHA base plus ERA, composites, side skirts and engine bay liner): 21.5t (19.5mt)
Calculated mass: 41.9t (38mt)
Crew: 4 (commander, gunner, loader, driver)
Length: 246" (6.25m) hull, 261" (6.62m) total 
Width:  150" (3.8m) with skirt
Height: 86" (2.19m) to top of commander's hatch, 91" (2.30m) total
 

 
Firepower
 
Note: the armour used for the target has the same hardness (360BRN) as the armour used in the vehicle. The target was at 0 degree obliquity for calculation purposes.
 
Main gun: 102mm L/40 “4-inch 40 calibre” low-pressure gun:
“Low-pressure” = 310 MPa/3.45MJ
“Emergency” pressure = 345MPa/3.83MJ
Recoil stroke: 300mm
Vertical travel: +20/-10’
 
Ammunition:
23.9lb (10.85kg) HEAT-FS, penetration of around 16.9" (430mm) using 122mm BK13 derivative (337mm if using BK13 penetration), 2614fps (797m/s). 26.2lb (11.90kg) HE, 2.92kg fill, estimated blast penetration of ~1.4" (35mm) RHA, 2496fps (761m/s). Simple APFSDS (15:1 LD, 550BHN monosteel body, tungsten insert, 76mm cap, ring sabot): 1x15.2" (26x387mm) rod, 0.55/3.4" (14x86mm) insert, 3.4/1.9lb (1.53/0.84kg) penetrator/sabot mass, 1800m/s, 10.3/9"(261/228mm) penetration at 100/2000y. Uses emergency pressure.  
Case: 4x19.7" (102x500mm) steel case, 4.7" (120mm base), OAL (HEAT-FS) = ~28" (700mm) Charge weight: 4.9lb (~2.2kg) standard, 5.4lb (2.46kg) emergency Case weight: 11.5lb (5.2kg) Overall weight (HEAT-FS): 40lb (18.25kg)  
Note: if following the design of 3BM-26, this could be higher in practice. Using DeMarre the estimated penetration is 10.8" (274mm) at 2000y.
 
Storage:
21 rounds stored in an armoured storage bin in the turret. The bin exhausts through blow-off panels in the turret side and roof.
36 rounds stored in armoured bins on either side of the driver behind the fuel cells, with blow-off panels in the hull side and front
 
Secondary weapons: 
.30cal/7.62mm MG as coax
Both the commander and loader’s hatch rotate and have mounts for .30 cal MGs.
 
Fire control:
Single axis stabilized gunner’s sight (of the same configuration as Derebus).
Backup 60mm telescopic sight mounted to mantlet.
Duel axis stabilized main gun.
LRF (of the same configuration as Derebus) mounted above barrel.
 

 
Mobility
 
2xV6 liquid-cooled diesels, 19l displacement each: 290hp/ 216kW each, 553kg dry weight each.
Combined output to hydraulic torque converter, feeding into Merritt-Brown-style double differential system.
The engine, transmission and cooling system all sit in an aluminium tub that fits into a bay in the rear of the vehicle. This can be removed entirely for servicing, or to replace the powerpack with a different configuration.
Suspension: 20" (0.5m) ground clearance, geared torsion bar suspension, each axle pair in detachable units shrouded by aluminium housings. Wheels are 23.6" (0.6m) in diameter, with a track width of 27.6" (0.7m) and a pitch of 7.7" (0.195m).
PWR: 13.8 HP/t (11.4 kW/mt)
Fuel load: ~2550lb total (793lb/360kg in tanks flanking the driver, 1764lb/800kg in rear sponson tanks, range of 540mi at 30mph
Ground pressure (calculated MMP): 28.4 PSI (196 KPa). 
Track contact length: 153.5” (3.9m)
Track contact area: 58.8ft2 (5.46m2)
Nominal ground pressure (using calculated mass): 9.86 PSI (68KPa)
 


 
Protection
 
 
Notes:
Mounting bolts for ERA layers are not modelled, but are accounted for.
The covers over the rear fuel cells are 1" RHA.
 
Turret front:
Two layers of L-ERA, sloped at 75’
Base armour: 3.15" (80mm) RHA sloped at 75’
KE: 18.3" (465mm)
CE: 104" (2650mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/12" (455/305mm), corresponding to 3"/3" high/low-precision charges and a 4" form factor.
 
Turret cheeks:
 
Note: because of how the cheeks are sloped, protection actually drops off the closer you get to the 25’ arc.
 
Three layers of L-ERA sloped at 25’ in the horizontal
Base armour: 3.15" (80mm RHA), sloped at 25’ in the horizontal
KE: 12" (305mm) from the front
CE: 56" (1425mm) (normal) vs single charge. Tandem charge rated to penetrate both layers via precursor is something like 12.2/7.3" (310/185mm), corresponding to 2.1/2.4" (55/60mm) high/low-precision charges and a 3" form factor.
 
Turret side armour array:
Two layers of L-ERA sloped at ~30’ in the horizontal
Base armour: 1" (25mm) RHA, sloped at ~30’ in the horizontal
KE: 5.9" (105mm) at 30’ from side.
CE: 13.4" (215mm) at 30' from side. Maximum angle that side can resist 7" CE is ~58' from the side (32' from the front).
 
 
Turret rear:
1.38" (35mm) RHA
 
Turret roof:
1" (25mm) RHA
 
Hull upper front:
Two layers of L-ERA, sloped at 75’
Base armour: 3.15" (80mm) RHA sloped at 75’
KE: 18.3" (465mm)
CE: 104" (2650mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/12" (455/305mm), corresponding to 3"/3" high/low-precision charges and a 4" form factor.
 
Hull lower front:
Base armour: 5.15" (131mm) RHA sloped at 45’ from vertical
KE: 7.3" (185mm)
CE: 7.3" (185mm) vs single-charge.
Notes: the area next to the driver contains two fuel cells and two protected storage areas for ammunition. Hits here are correspondingly much more protected than the above would indicate, for both the upper and lower hull.
 
Hull side:
2 x L-ERA layers
25mm RHA skirt
1" (25mm) aluminium roadwheel (depending on hit location)
29.5" (750mm) air gap/fuel (depending on hit location)
Inner skin: 1" (25mm) RHA
KE: ~3.5" (85-95mm) (normal) / ~9" (210-245mm) (30’ arc from the front)
CE: ~4.2" (100-115mm) (normal) / ~32" (730-890) (30’ arc from the front)
Immunity zone against 15.7" KE: 21’ arc from front
Immunity zone against 7" CE: 56’ from front (34' from the side)
 
Notes: the upper hull side has numerous armoured brackets to hold the skirt. These would be expected to be hit when the impact is from the 30' arc, which would significantly improve protection.
 
Belly:
1" 25mm RHA
0-0.8" aluminium
 
Notes: the suspension units are aluminium boxes, the torsion bars are modelled as 2.75" (70mm) bars and each swing arm is attached to a hollow steel tube. The mine protection for the floor of the vehicle is accordingly expected to be much higher than these figures would indicate.
 


 

After finishing up on Derebus, the good folk at Para-allful Conglomerated decided to make a simplified model for the more down-scale customer:

The Derebus-M uses the 4" 40 cal low-pressure gun in an all-new turret. This, along with removing some of the nice-to-haves such as the coincidence rangefinder, complex fire control system and composite internal armour panels, allows the Derebus-M to be made cheaper, simpler and a bit lighter.

Final Entry: Main Battle Tank, 2247, project name "Derebus"
 

 
Main dimensions and statistics
Manufacturer: Paramount-Allen-Fullerton (Para-allful) Conglomerated Mass estimate (as based on CAD model plus ~6600lb to account for drive systems, crew amenities, ammunition and miscellaneous components): 43.1t (39.1mt) fully loaded, fueled. Armour mass (1-2" (25-50mm) RHA base plus ERA, composites, side skirts and engine bay liner): 20.6t (18.5mt) Calculated mass: 43.4t (39.4mt) Crew: 4 (commander, gunner, loader, driver) Length: 246" (6.25m) hull, 379" (9.63m) total  Width:  150" (3.8m) with skirt Height: 95" (2.41m) to top of commander's hatch, 109" (2.77m) total  

Firepower

Note: the armour used for the target has the same hardness (360BRN) as the armour used in the vehicle. The target was at 0 degree obliquity for calculation purposes.
 
Main gun: 5-inch 55 calibre (127mm L/55) high/low pressure gun “High pressure” = 70000 PSI (480 MPa) operating pressure, 14.16MJ energy. Vertical travel: +15'/-10'  
Ammunition:
46lb (20.85kg) HEAT-FS, penetration of around 21" (535mm) using 122mm BK13 derivative (420mm if using BK13 penetration), 3074fps (937m/s), 9.14MJ using a low-pressure charge (~45k PSI). 46lb (23.2kg) HE, (5.7kg) fill, estimated blast penetration of ~55mm RHA, 2910fps (887m/s) Simple APFSDS (15:1 LD, 550BHN monosteel body, tungsten insert, 115mm cap, ring sabot): 1.57x23.54" (40x597mm) rod, 0.866x5.24" (22x133mm) insert, 14.2/5.2lb (5.6/3.2kg) penetrator/sabot mass, 1800m/s, 15.7/13.8" (400/350mm) penetration at 100/2000y.  
Note: if following the design of 3BM-26, this could be higher in practice. Using DeMarre the estimated penetration is 17.1" (435mm) at 2000y. Upgraded monobloc projectiles could match and eventually improve on this, up to 25.6" (650mm) before needing to rework the ammunition storage.
 
Details:
 
Gun has a high-pressure and low-pressure recoil option, selectable on the slide – this doesn’t affect the recoil mechanism, it just changes where the trip key is to unlock the breech. Warning: don’t fire high-pressure ammo with the low-pressure setting selected! Gun uses a separate 6.9x27" (175x685mm) charge: 44lb/20kg mass, semi-combustible case built along the lines of the 4Zh-40 charge used with the 2A26 gun), matching the length of the HEAT-FS round. This charge gives space to produce a more powerful round to match higher future barrel higher pressures (when using a secondary charge with the APFSDS projectile itself). 74000 PSI (510 MPa) gives a potential power of 15MJ. 94000PSI (650 MPa) gives a potential power of 19MJ. Final penetration potential of the gun with early monobloc DU projectiles is something in the region of 22" (550mm) at 2000y (putting it on par with Mango and Vant). Being able to store and handle a longer projectile (ie: above 27") would probably allow something a bit better than Snivets.  Low-pressure charges are shortened (17.1" / 435mm) and come with an ejection spring to work with the same tubes as the high-pressure charges.  
Storage:
19 charges and 9 active projectiles (HE and HEAT) in armoured tubes in the turret. The tubes are sealed at the front and lead to a blast chimney that outlets to blow-off panels in the turret roof. 10 inert projectiles (APFSDS) are stored in various places in the turret space, held by retaining clips. 16 charges and 8 active projectiles are stored on either side of the driver behind the fuel cells, also using the blast chimney approach (exhausting out the hull sides). 8 inert projectiles are stored in various spots in the hull.  
Secondary weapons: 
.30cal MG as coax Both the commander and loader’s hatch rotate and have mounts for .30 cal MGs.  
Fire control:
Single axis stabilized gunner’s sight Duel axis stabilized main gun Vertical coincidence rangefinder (stadiametric, 39.4" (1m) base) which doubles as a redundant back-up sight. Simple electronic gun-follows sight fire control system (encoder connected to sight mirror feeds elevation data into a transistor-based PID controller, which tries to match position on a similar encoder connected to the gun. When gun position and sight position align, the firing mechanism is electronically triggered). Semi-autoloader: the loader places the charge and warhead on trays in the bustle. these are then fed into the gun using an automatic mechanism (horizontal rammer, pivoting loading tray and rigid chain actuator to ram the warhead and charge home). The gun automatically returns to the loading position after each shot. A short spring at the end of the actuator helps to smooth out the loading impulse. LRF mounted above barrel.  
Note: Industrial espionage has allowed Texan engineers to copy the laser rangefinder proposed for use in the Cascadian M8A1 upgrade package. The Texan copy of the LRS-2 ruby laser rangefinder uses a flashlamp-pumped ruby laser, optical sensor, quartz timing circuit and the sequential event time sampling approach (with post-sampling amplification) to allow time-of-flight rangefinding using a lower timebase and bandwidth compatible with current electronics. Solid state electronic components allow the system to be fairly compact and robust. The rangefinder features a numerical readout in the gunner’s station. The rangefinder has a maximum operating range of 5km in clear conditions and has an average estimation error of 1%. 
 
The TBC-3A ballistic computer and IAPO-3 sight were not copied, as the high velocity of the APFSDS used in the 5”/55 cal main gun was felt to provide sufficient accuracy when paired with a good rangefinder.
 
Mobility

Transverse-mounted Kharkiv V-2-derived engine (specifically the V-55 diesel): 600HP/448kW, 2248lb/1020kg dry weight. The engine has been slightly re-bored to 40l, but is otherwise mechanically very similar to the engine used on the historical T-62. Hydraulic torque converter feeding into Merritt-Brown-style double differential system. An alternate engine layout would be two V-6 engines of similar total displacement, mounted normally, with a combined linkage to the torque converter. The engine, transmission and cooling system all sit in an aluminium tub that fits into a bay in the rear of the vehicle. This can be removed entirely for servicing, or to replace the powerpack with a different configuration. Suspension: 20" (0.5m) ground clearance, geared torsion bar suspension, each axle pair in detachable units shrouded by aluminium housings. Wheels are 23.6" (0.6m) in diameter, with a track width of 27.6" (0.7m) and a pitch of 7.7" (0.195m). Fuel load: ~2400lb total (639lb/290kg in tanks flanking the driver, 1764lb/800kg in rear sponson tanks, range of 490mi at 30mph PWR: 13.8 HP/t (11.4 kW/mt) Ground pressure (calculated MMP): 29.4 PSI (203 KPa).  Track contact length: 153.5" (3.9m) Track contact area: 58.8ft2 (5.46m2) Nominal ground pressure (based on calculated weight): 10.3 PSI (70.77 KPa)  
Protection


Notes:
Composite liner (50:50 HHA/textolite): density of 4.825g/cm3, layers of 0.2, 0.4, 0.6, 0.8 or 1" depending, with thickness adjusted to prefer the thickest possible layers (1"/1") with a thinner backing layer. Mounting bolts for ERA layers are not modelled, but are accounted for. The covers over the rear fuel cells are 1" RHA.  
Turret front:
Two layers of L-ERA, sloped at 75’ Base armour: 1" (25mm) RHA sloped at 75’ 2.1" (55mm) composite (25mm HHA, 25mm textolite), sloped at 75’ KE: 16.9" (430mm) CE: 89" (2250mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/11.4" (455/290mm), corresponding to 3"/3" high/low-precision charges and a 4" form factor.  
Turret cheeks:
 
Note: because of how the cheeks are sloped, protection actually drops off the closer you get to the 25’ arc.
 
Three layers of L-ERA sloped at 25’ in the horizontal Base armour: 1" (25mm RHA), sloped at 25’ in the horizontal 2.2" (55mm) composite, sloped at 25’ in the horizontal KE: 11.4" (290mm) from the front CE: 55" (1400mm) (normal) vs single charge. Tandem charge rated to penetrate both layers via precursor is something like 12.2/7.3" (310/185mm), corresponding to 2.1/2.4" (55/60mm) high/low-precision charges and a 3" form factor.  
Turret side armour array:
Two layers of L-ERA sloped at ~30’ in the horizontal Base armour: 1" (25mm) RHA, sloped at ~30’ in the horizontal 1" (25mm) composite, sloped at 30’ in the horizontal KE: 5.9" (150mm) at 30’ from side. CE: 13.4" (340mm) at 30' from side. Maximum angle that side can resist 7" CE is ~20' from the side (70' from the front).  
 
Turret rear:
2" (50mm) RHA  
Turret roof:
1" (25mm) RHA  
Hull upper front:
Two layers of L-ERA, sloped at 75’ Base armour: 1" (25mm) RHA sloped at 75’ 2.2" (55mm) composite, sloped at 75’ KE: 16.9" (430mm) CE: 89" (2250mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/11.4" (455/290mm), corresponding to 3" high/low-precision charges and a 4" form factor.  
Hull lower front:
Base armour: 1" (25mm) RHA sloped at 45’ from vertical 4.2" (106mm) composite, sloped at 45’ from vertical KE: 7.3" (185mm) CE: 7.5" (190mm) vs single-charge. Notes: the area next to the driver contains two fuel cells and two protected storage areas for ammunition. Hits here are correspondingly much more protected than the above would indicate, for both the upper and lower hull.
 
Hull side:
2 x L-ERA layers Composite skirt: 0.2" (5mm) HHA with a 0.8" (20mm) textolite backing 1" (25mm) aluminium roadwheel (depending on hit location) 29.5" (750mm) air gap/fuel (depending on hit location) Inner skin: 1" (25mm) RHA KE: ~3" (75-80mm) (normal) / ~8.2" (190-225mm) (30’ arc from the front) CE: ~3.8" (95-100mm) (normal) / ~30" (690-860) (30’ arc from the front) Immunity zone against 15.7" KE: 21’ arc from front Immunity zone against 7" CE: 54’ from front (36' from the side)  
Notes: the upper hull side has numerous armoured brackets to hold the skirt. These would be expected to be hit when the impact is from the 30' arc, which would significantly improve protection.
 
Belly:
1" 25mm RHA 0-0.8" aluminium  
Notes: the suspension units are aluminium boxes, the torsion bars are modelled as 2.75" (70mm) bars and each swing arm is attached to a hollow steel tube. The mine protection for the floor of the vehicle is accordingly expected to be much higher than these figures would indicate.

TIL that sauropods had terrifying nightmare feet:
 
 

After finishing up on Derebus, the good folk at Para-allful Conglomerated decided to make a simplified model for the more down-scale customer:

The Derebus-M uses the 4" 40 cal low-pressure gun in an all-new turret. This, along with removing some of the nice-to-haves such as the coincidence rangefinder, complex fire control system and composite internal armour panels, allows the Derebus-M to be made cheaper, simpler and a bit lighter.

Final Entry: Main Battle Tank, 2247, project name "Derebus"
 

 
Main dimensions and statistics
Manufacturer: Paramount-Allen-Fullerton (Para-allful) Conglomerated Mass estimate (as based on CAD model plus ~6600lb to account for drive systems, crew amenities, ammunition and miscellaneous components): 43.1t (39.1mt) fully loaded, fueled. Armour mass (1-2" (25-50mm) RHA base plus ERA, composites, side skirts and engine bay liner): 20.6t (18.5mt) Calculated mass: 43.4t (39.4mt) Crew: 4 (commander, gunner, loader, driver) Length: 246" (6.25m) hull, 379" (9.63m) total  Width:  150" (3.8m) with skirt Height: 95" (2.41m) to top of commander's hatch, 109" (2.77m) total  

Firepower

Note: the armour used for the target has the same hardness (360BRN) as the armour used in the vehicle. The target was at 0 degree obliquity for calculation purposes.
 
Main gun: 5-inch 55 calibre (127mm L/55) high/low pressure gun “High pressure” = 70000 PSI (480 MPa) operating pressure, 14.16MJ energy. Vertical travel: +15'/-10'  
Ammunition:
46lb (20.85kg) HEAT-FS, penetration of around 21" (535mm) using 122mm BK13 derivative (420mm if using BK13 penetration), 3074fps (937m/s), 9.14MJ using a low-pressure charge (~45k PSI). 46lb (23.2kg) HE, (5.7kg) fill, estimated blast penetration of ~55mm RHA, 2910fps (887m/s) Simple APFSDS (15:1 LD, 550BHN monosteel body, tungsten insert, 115mm cap, ring sabot): 1.57x23.54" (40x597mm) rod, 0.866x5.24" (22x133mm) insert, 14.2/5.2lb (5.6/3.2kg) penetrator/sabot mass, 1800m/s, 15.7/13.8" (400/350mm) penetration at 100/2000y.  
Note: if following the design of 3BM-26, this could be higher in practice. Using DeMarre the estimated penetration is 17.1" (435mm) at 2000y. Upgraded monobloc projectiles could match and eventually improve on this, up to 25.6" (650mm) before needing to rework the ammunition storage.
 
Details:
 
Gun has a high-pressure and low-pressure recoil option, selectable on the slide – this doesn’t affect the recoil mechanism, it just changes where the trip key is to unlock the breech. Warning: don’t fire high-pressure ammo with the low-pressure setting selected! Gun uses a separate 6.9x27" (175x685mm) charge: 44lb/20kg mass, semi-combustible case built along the lines of the 4Zh-40 charge used with the 2A26 gun), matching the length of the HEAT-FS round. This charge gives space to produce a more powerful round to match higher future barrel higher pressures (when using a secondary charge with the APFSDS projectile itself). 74000 PSI (510 MPa) gives a potential power of 15MJ. 94000PSI (650 MPa) gives a potential power of 19MJ. Final penetration potential of the gun with early monobloc DU projectiles is something in the region of 22" (550mm) at 2000y (putting it on par with Mango and Vant). Being able to store and handle a longer projectile (ie: above 27") would probably allow something a bit better than Snivets.  Low-pressure charges are shortened (17.1" / 435mm) and come with an ejection spring to work with the same tubes as the high-pressure charges.  
Storage:
19 charges and 9 active projectiles (HE and HEAT) in armoured tubes in the turret. The tubes are sealed at the front and lead to a blast chimney that outlets to blow-off panels in the turret roof. 10 inert projectiles (APFSDS) are stored in various places in the turret space, held by retaining clips. 16 charges and 8 active projectiles are stored on either side of the driver behind the fuel cells, also using the blast chimney approach (exhausting out the hull sides). 8 inert projectiles are stored in various spots in the hull.  
Secondary weapons: 
.30cal MG as coax Both the commander and loader’s hatch rotate and have mounts for .30 cal MGs.  
Fire control:
Single axis stabilized gunner’s sight Duel axis stabilized main gun Vertical coincidence rangefinder (stadiametric, 39.4" (1m) base) which doubles as a redundant back-up sight. Simple electronic gun-follows sight fire control system (encoder connected to sight mirror feeds elevation data into a transistor-based PID controller, which tries to match position on a similar encoder connected to the gun. When gun position and sight position align, the firing mechanism is electronically triggered). Semi-autoloader: the loader places the charge and warhead on trays in the bustle. these are then fed into the gun using an automatic mechanism (horizontal rammer, pivoting loading tray and rigid chain actuator to ram the warhead and charge home). The gun automatically returns to the loading position after each shot. A short spring at the end of the actuator helps to smooth out the loading impulse. LRF mounted above barrel.  
Note: Industrial espionage has allowed Texan engineers to copy the laser rangefinder proposed for use in the Cascadian M8A1 upgrade package. The Texan copy of the LRS-2 ruby laser rangefinder uses a flashlamp-pumped ruby laser, optical sensor, quartz timing circuit and the sequential event time sampling approach (with post-sampling amplification) to allow time-of-flight rangefinding using a lower timebase and bandwidth compatible with current electronics. Solid state electronic components allow the system to be fairly compact and robust. The rangefinder features a numerical readout in the gunner’s station. The rangefinder has a maximum operating range of 5km in clear conditions and has an average estimation error of 1%. 
 
The TBC-3A ballistic computer and IAPO-3 sight were not copied, as the high velocity of the APFSDS used in the 5”/55 cal main gun was felt to provide sufficient accuracy when paired with a good rangefinder.
 
Mobility

Transverse-mounted Kharkiv V-2-derived engine (specifically the V-55 diesel): 600HP/448kW, 2248lb/1020kg dry weight. The engine has been slightly re-bored to 40l, but is otherwise mechanically very similar to the engine used on the historical T-62. Hydraulic torque converter feeding into Merritt-Brown-style double differential system. An alternate engine layout would be two V-6 engines of similar total displacement, mounted normally, with a combined linkage to the torque converter. The engine, transmission and cooling system all sit in an aluminium tub that fits into a bay in the rear of the vehicle. This can be removed entirely for servicing, or to replace the powerpack with a different configuration. Suspension: 20" (0.5m) ground clearance, geared torsion bar suspension, each axle pair in detachable units shrouded by aluminium housings. Wheels are 23.6" (0.6m) in diameter, with a track width of 27.6" (0.7m) and a pitch of 7.7" (0.195m). Fuel load: ~2400lb total (639lb/290kg in tanks flanking the driver, 1764lb/800kg in rear sponson tanks, range of 490mi at 30mph PWR: 13.8 HP/t (11.4 kW/mt) Ground pressure (calculated MMP): 29.4 PSI (203 KPa).  Track contact length: 153.5" (3.9m) Track contact area: 58.8ft2 (5.46m2) Nominal ground pressure (based on calculated weight): 10.3 PSI (70.77 KPa)  
Protection


Notes:
Composite liner (50:50 HHA/textolite): density of 4.825g/cm3, layers of 0.2, 0.4, 0.6, 0.8 or 1" depending, with thickness adjusted to prefer the thickest possible layers (1"/1") with a thinner backing layer. Mounting bolts for ERA layers are not modelled, but are accounted for. The covers over the rear fuel cells are 1" RHA.  
Turret front:
Two layers of L-ERA, sloped at 75’ Base armour: 1" (25mm) RHA sloped at 75’ 2.1" (55mm) composite (25mm HHA, 25mm textolite), sloped at 75’ KE: 16.9" (430mm) CE: 89" (2250mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/11.4" (455/290mm), corresponding to 3"/3" high/low-precision charges and a 4" form factor.  
Turret cheeks:
 
Note: because of how the cheeks are sloped, protection actually drops off the closer you get to the 25’ arc.
 
Three layers of L-ERA sloped at 25’ in the horizontal Base armour: 1" (25mm RHA), sloped at 25’ in the horizontal 2.2" (55mm) composite, sloped at 25’ in the horizontal KE: 11.4" (290mm) from the front CE: 55" (1400mm) (normal) vs single charge. Tandem charge rated to penetrate both layers via precursor is something like 12.2/7.3" (310/185mm), corresponding to 2.1/2.4" (55/60mm) high/low-precision charges and a 3" form factor.  
Turret side armour array:
Two layers of L-ERA sloped at ~30’ in the horizontal Base armour: 1" (25mm) RHA, sloped at ~30’ in the horizontal 1" (25mm) composite, sloped at 30’ in the horizontal KE: 5.9" (150mm) at 30’ from side. CE: 13.4" (340mm) at 30' from side. Maximum angle that side can resist 7" CE is ~20' from the side (70' from the front).  
 
Turret rear:
2" (50mm) RHA  
Turret roof:
1" (25mm) RHA  
Hull upper front:
Two layers of L-ERA, sloped at 75’ Base armour: 1" (25mm) RHA sloped at 75’ 2.2" (55mm) composite, sloped at 75’ KE: 16.9" (430mm) CE: 89" (2250mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/11.4" (455/290mm), corresponding to 3" high/low-precision charges and a 4" form factor.  
Hull lower front:
Base armour: 1" (25mm) RHA sloped at 45’ from vertical 4.2" (106mm) composite, sloped at 45’ from vertical KE: 7.3" (185mm) CE: 7.5" (190mm) vs single-charge. Notes: the area next to the driver contains two fuel cells and two protected storage areas for ammunition. Hits here are correspondingly much more protected than the above would indicate, for both the upper and lower hull.
 
Hull side:
2 x L-ERA layers Composite skirt: 0.2" (5mm) HHA with a 0.8" (20mm) textolite backing 1" (25mm) aluminium roadwheel (depending on hit location) 29.5" (750mm) air gap/fuel (depending on hit location) Inner skin: 1" (25mm) RHA KE: ~3" (75-80mm) (normal) / ~8.2" (190-225mm) (30’ arc from the front) CE: ~3.8" (95-100mm) (normal) / ~30" (690-860) (30’ arc from the front) Immunity zone against 15.7" KE: 21’ arc from front Immunity zone against 7" CE: 54’ from front (36' from the side)  
Notes: the upper hull side has numerous armoured brackets to hold the skirt. These would be expected to be hit when the impact is from the 30' arc, which would significantly improve protection.
 
Belly:
1" 25mm RHA 0-0.8" aluminium  
Notes: the suspension units are aluminium boxes, the torsion bars are modelled as 2.75" (70mm) bars and each swing arm is attached to a hollow steel tube. The mine protection for the floor of the vehicle is accordingly expected to be much higher than these figures would indicate.

Final Entry: Main Battle Tank, 2247, project name "Derebus"
 

 
Main dimensions and statistics
Manufacturer: Paramount-Allen-Fullerton (Para-allful) Conglomerated Mass estimate (as based on CAD model plus ~6600lb to account for drive systems, crew amenities, ammunition and miscellaneous components): 43.1t (39.1mt) fully loaded, fueled. Armour mass (1-2" (25-50mm) RHA base plus ERA, composites, side skirts and engine bay liner): 20.6t (18.5mt) Calculated mass: 43.4t (39.4mt) Crew: 4 (commander, gunner, loader, driver) Length: 246" (6.25m) hull, 379" (9.63m) total  Width:  150" (3.8m) with skirt Height: 95" (2.41m) to top of commander's hatch, 109" (2.77m) total  

Firepower

Note: the armour used for the target has the same hardness (360BRN) as the armour used in the vehicle. The target was at 0 degree obliquity for calculation purposes.
 
Main gun: 5-inch 55 calibre (127mm L/55) high/low pressure gun “High pressure” = 70000 PSI (480 MPa) operating pressure, 14.16MJ energy. Vertical travel: +15'/-10'  
Ammunition:
46lb (20.85kg) HEAT-FS, penetration of around 21" (535mm) using 122mm BK13 derivative (420mm if using BK13 penetration), 3074fps (937m/s), 9.14MJ using a low-pressure charge (~45k PSI). 46lb (23.2kg) HE, (5.7kg) fill, estimated blast penetration of ~55mm RHA, 2910fps (887m/s) Simple APFSDS (15:1 LD, 550BHN monosteel body, tungsten insert, 115mm cap, ring sabot): 1.57x23.54" (40x597mm) rod, 0.866x5.24" (22x133mm) insert, 14.2/5.2lb (5.6/3.2kg) penetrator/sabot mass, 1800m/s, 15.7/13.8" (400/350mm) penetration at 100/2000y.  
Note: if following the design of 3BM-26, this could be higher in practice. Using DeMarre the estimated penetration is 17.1" (435mm) at 2000y. Upgraded monobloc projectiles could match and eventually improve on this, up to 25.6" (650mm) before needing to rework the ammunition storage.
 
Details:
 
Gun has a high-pressure and low-pressure recoil option, selectable on the slide – this doesn’t affect the recoil mechanism, it just changes where the trip key is to unlock the breech. Warning: don’t fire high-pressure ammo with the low-pressure setting selected! Gun uses a separate 6.9x27" (175x685mm) charge: 44lb/20kg mass, semi-combustible case built along the lines of the 4Zh-40 charge used with the 2A26 gun), matching the length of the HEAT-FS round. This charge gives space to produce a more powerful round to match higher future barrel higher pressures (when using a secondary charge with the APFSDS projectile itself). 74000 PSI (510 MPa) gives a potential power of 15MJ. 94000PSI (650 MPa) gives a potential power of 19MJ. Final penetration potential of the gun with early monobloc DU projectiles is something in the region of 22" (550mm) at 2000y (putting it on par with Mango and Vant). Being able to store and handle a longer projectile (ie: above 27") would probably allow something a bit better than Snivets.  Low-pressure charges are shortened (17.1" / 435mm) and come with an ejection spring to work with the same tubes as the high-pressure charges.  
Storage:
19 charges and 9 active projectiles (HE and HEAT) in armoured tubes in the turret. The tubes are sealed at the front and lead to a blast chimney that outlets to blow-off panels in the turret roof. 10 inert projectiles (APFSDS) are stored in various places in the turret space, held by retaining clips. 16 charges and 8 active projectiles are stored on either side of the driver behind the fuel cells, also using the blast chimney approach (exhausting out the hull sides). 8 inert projectiles are stored in various spots in the hull.  
Secondary weapons: 
.30cal MG as coax Both the commander and loader’s hatch rotate and have mounts for .30 cal MGs.  
Fire control:
Single axis stabilized gunner’s sight Duel axis stabilized main gun Vertical coincidence rangefinder (stadiametric, 39.4" (1m) base) which doubles as a redundant back-up sight. Simple electronic gun-follows sight fire control system (encoder connected to sight mirror feeds elevation data into a transistor-based PID controller, which tries to match position on a similar encoder connected to the gun. When gun position and sight position align, the firing mechanism is electronically triggered). Semi-autoloader: the loader places the charge and warhead on trays in the bustle. these are then fed into the gun using an automatic mechanism (horizontal rammer, pivoting loading tray and rigid chain actuator to ram the warhead and charge home). The gun automatically returns to the loading position after each shot. A short spring at the end of the actuator helps to smooth out the loading impulse. LRF mounted above barrel.  
Note: Industrial espionage has allowed Texan engineers to copy the laser rangefinder proposed for use in the Cascadian M8A1 upgrade package. The Texan copy of the LRS-2 ruby laser rangefinder uses a flashlamp-pumped ruby laser, optical sensor, quartz timing circuit and the sequential event time sampling approach (with post-sampling amplification) to allow time-of-flight rangefinding using a lower timebase and bandwidth compatible with current electronics. Solid state electronic components allow the system to be fairly compact and robust. The rangefinder features a numerical readout in the gunner’s station. The rangefinder has a maximum operating range of 5km in clear conditions and has an average estimation error of 1%. 
 
The TBC-3A ballistic computer and IAPO-3 sight were not copied, as the high velocity of the APFSDS used in the 5”/55 cal main gun was felt to provide sufficient accuracy when paired with a good rangefinder.
 
Mobility

Transverse-mounted Kharkiv V-2-derived engine (specifically the V-55 diesel): 600HP/448kW, 2248lb/1020kg dry weight. The engine has been slightly re-bored to 40l, but is otherwise mechanically very similar to the engine used on the historical T-62. Hydraulic torque converter feeding into Merritt-Brown-style double differential system. An alternate engine layout would be two V-6 engines of similar total displacement, mounted normally, with a combined linkage to the torque converter. The engine, transmission and cooling system all sit in an aluminium tub that fits into a bay in the rear of the vehicle. This can be removed entirely for servicing, or to replace the powerpack with a different configuration. Suspension: 20" (0.5m) ground clearance, geared torsion bar suspension, each axle pair in detachable units shrouded by aluminium housings. Wheels are 23.6" (0.6m) in diameter, with a track width of 27.6" (0.7m) and a pitch of 7.7" (0.195m). Fuel load: ~2400lb total (639lb/290kg in tanks flanking the driver, 1764lb/800kg in rear sponson tanks, range of 490mi at 30mph PWR: 13.8 HP/t (11.4 kW/mt) Ground pressure (calculated MMP): 29.4 PSI (203 KPa).  Track contact length: 153.5" (3.9m) Track contact area: 58.8ft2 (5.46m2) Nominal ground pressure (based on calculated weight): 10.3 PSI (70.77 KPa)  
Protection


Notes:
Composite liner (50:50 HHA/textolite): density of 4.825g/cm3, layers of 0.2, 0.4, 0.6, 0.8 or 1" depending, with thickness adjusted to prefer the thickest possible layers (1"/1") with a thinner backing layer. Mounting bolts for ERA layers are not modelled, but are accounted for. The covers over the rear fuel cells are 1" RHA.  
Turret front:
Two layers of L-ERA, sloped at 75’ Base armour: 1" (25mm) RHA sloped at 75’ 2.1" (55mm) composite (25mm HHA, 25mm textolite), sloped at 75’ KE: 16.9" (430mm) CE: 89" (2250mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/11.4" (455/290mm), corresponding to 3"/3" high/low-precision charges and a 4" form factor.  
Turret cheeks:
 
Note: because of how the cheeks are sloped, protection actually drops off the closer you get to the 25’ arc.
 
Three layers of L-ERA sloped at 25’ in the horizontal Base armour: 1" (25mm RHA), sloped at 25’ in the horizontal 2.2" (55mm) composite, sloped at 25’ in the horizontal KE: 11.4" (290mm) from the front CE: 55" (1400mm) (normal) vs single charge. Tandem charge rated to penetrate both layers via precursor is something like 12.2/7.3" (310/185mm), corresponding to 2.1/2.4" (55/60mm) high/low-precision charges and a 3" form factor.  
Turret side armour array:
Two layers of L-ERA sloped at ~30’ in the horizontal Base armour: 1" (25mm) RHA, sloped at ~30’ in the horizontal 1" (25mm) composite, sloped at 30’ in the horizontal KE: 5.9" (150mm) at 30’ from side. CE: 13.4" (340mm) at 30' from side. Maximum angle that side can resist 7" CE is ~20' from the side (70' from the front).  
 
Turret rear:
2" (50mm) RHA  
Turret roof:
1" (25mm) RHA  
Hull upper front:
Two layers of L-ERA, sloped at 75’ Base armour: 1" (25mm) RHA sloped at 75’ 2.2" (55mm) composite, sloped at 75’ KE: 16.9" (430mm) CE: 89" (2250mm) vs single-charge. Tandem charge rated to penetrate both layers via precursor is something like 17.9/11.4" (455/290mm), corresponding to 3" high/low-precision charges and a 4" form factor.  
Hull lower front:
Base armour: 1" (25mm) RHA sloped at 45’ from vertical 4.2" (106mm) composite, sloped at 45’ from vertical KE: 7.3" (185mm) CE: 7.5" (190mm) vs single-charge. Notes: the area next to the driver contains two fuel cells and two protected storage areas for ammunition. Hits here are correspondingly much more protected than the above would indicate, for both the upper and lower hull.
 
Hull side:
2 x L-ERA layers Composite skirt: 0.2" (5mm) HHA with a 0.8" (20mm) textolite backing 1" (25mm) aluminium roadwheel (depending on hit location) 29.5" (750mm) air gap/fuel (depending on hit location) Inner skin: 1" (25mm) RHA KE: ~3" (75-80mm) (normal) / ~8.2" (190-225mm) (30’ arc from the front) CE: ~3.8" (95-100mm) (normal) / ~30" (690-860) (30’ arc from the front) Immunity zone against 15.7" KE: 21’ arc from front Immunity zone against 7" CE: 54’ from front (36' from the side)  
Notes: the upper hull side has numerous armoured brackets to hold the skirt. These would be expected to be hit when the impact is from the 30' arc, which would significantly improve protection.
 
Belly:
1" 25mm RHA 0-0.8" aluminium  
Notes: the suspension units are aluminium boxes, the torsion bars are modelled as 2.75" (70mm) bars and each swing arm is attached to a hollow steel tube. The mine protection for the floor of the vehicle is accordingly expected to be much higher than these figures would indicate.

I've christened it "Derebus".
Armour package and hull/turret base altogether weigh 19.89t, putting me on track to hit my target weight of 41.3t.

I am going to be introducing a new recommended weight accounting method to help standardize results between contestants, and to better prepare them for the judges' ire. This method is not mandatory, however it is strongly recommended, as it is expected to be the method by which the judges weigh (literally) each entrant against each other.

First, we are requiring in addition to the standard elements included on the submission sheet, that you include the armor mass of your tank in your submission. The armor mass includes any armor elements of your tank, including in addition to armor arrays, also structural elements like a cast or welded hull body, skirts, armored engine decks, hatches, etc.

Next, to calculate the combat weight of your tank (as outlined in the submission template), you take the armor mass of your tank, and multiply it by 0.45 to get the mass of suspension components for your tank (this includes tracks, roadwheels, sprockets, swing arms, idler tensioners, return rollers, etc). The reason for doing this is that as suspended mass increases, the mass of the suspension must increase also, meaning that in successful tank designs this ratio of about 0.45 stays remarkably constant (as detailed in Technology of Tanks). Then, add the armor mass and the suspension mass together with these figures:

Gun weight: (variable)
Ammunition weight: (variable)
Ammunition racks weight: (variable, but in the absence of a modeled weight for them, 1,700 lbs is a fine figure)
Gun stabilization system and gun electrics: 1,700 lbs for a ~4.7 inch gun (cubic scaling according to caliber, with minimum of 1,000 lbs)
Engine weight: (variable)
Transmission weight: (variable)
Fuel weight: (variable, but if you haven't modeled it for your tank, then use the value required to meet the range requirement)
Fuel system weight: 750 lbs
Electrical and environmental systems (combined): 3,500 lbs
Optics, sighting: 300-500 lbs (depending on complexity)
Fitments, stowage, and installed equipment: 7,500 lbs
Any other objects you've modeled, like cupolas etc: (variable)
Crew: 265 lbs per crewman
 
This means that if I have modeled a tank's armor, which weighs 18 tons for the hull and 12 tons for the turret (including arrays, engine deck, armored hatches, etc), my math will look like this:
18 + 12 = 30 tons hull (incl. skirts) and turret
30 x 0.45 = 13.5 tons suspension
13.5 + 30 = 43.5 tons hull, turret, and suspension
43.5 * 2,205 = 95917.5 lbs hull, turret, and suspension
95917.5 +
5300 lbs gun
2,650 lbs ammunition
1,700 lbs ammo racks
2,000 lbs gun stabilization and electrics
4,950 lbs engine
5,400 lbs transmission and final drives
3,660 lbs fuel
750 lbs fuel system
3,500 lbs electrical and environmental
500 lbs optics
7,500 lbs fitments, etc
265 lbs * 4 crew
=
134887.5 lbs combat weight for the tank, or 61.2 metric tons.
 

I've christened it "Derebus".
Armour package and hull/turret base altogether weigh 19.89t, putting me on track to hit my target weight of 41.3t.

I've christened it "Derebus".
Armour package and hull/turret base altogether weigh 19.89t, putting me on track to hit my target weight of 41.3t.

I've christened it "Derebus".
Armour package and hull/turret base altogether weigh 19.89t, putting me on track to hit my target weight of 41.3t.

I too have noticed this trend
 
 

This is FUTURE TEXAS, son. We measure our armour in fractions of 16ths of a mile and like it.

This is FUTURE TEXAS, son. We measure our armour in fractions of 16ths of a mile and like it.

This is FUTURE TEXAS, son. We measure our armour in fractions of 16ths of a mile and like it.

MUH NERA

 
Birgus, (or Lynx, don't know yet the name) the Fulda Gap fever dream: