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For the purposes of submission, I've now converted all the weights of my tanks to metric (I only noticed that tank designer's output is in short tonnes a few days ago) and for combat weight rather than empty weight.


I looked into a 35-tonne medium design, but it ended up being a T25 analogue with a conventional transmission so I didn't get much further than a spreadsheet design.

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On 8/25/2018 at 5:07 PM, Xoon said:

In pains me that I probably won't be able to throw my hat in the ring. But in case I get the chance, I have a few questions:

What is the average height of a conscript male?
What fuel does the enemy use?
Is the technology cut-off date 1969?
Is cast armor roughly 15% weaker?




Didn't see this earlier.

The loss of strength with castings is pretty variable.  I've seen estimates as low as 5% and as high as 50%, so it depends heavily on how proficient the foundries are.


On the credit side of the ledger, castings don't have any weaknesses caused by the Heat Affected Zone the way welds do.

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As I find myself in a bit of a time crunch, the light tank proposal will be quite a bit less fancy than the Norman.
The preliminary sketch is as follows:
8x8 or 6x6 wheeled deathtrap, with double wishbone steerable suspension on the first and fourth axles (if present), modified Christie on the second and third.
Armament is to be a low-pressure 90mm feeding from a 6-10 round autoloader (as a ready rack, with spare ammo) or a dual-feed 30mm modeled after the 2A42. A coax 7.62 is fitted in any case. Due to weight and volume considerations the 30mm turret is liable to come with more goodies than the 90. 30mm APDS and later APFSDS will kill any light vehicle which would theoretically be developed in the next few decades, while 90mm HEAT will be capable of killing heavy armor. 90mm HE will also be useful for fire support.
There is an additional armament component which will be expanded on later.
Proposed variants of this design are light/scout tank, FSV, APC (Saracen-style), SPAA and supply vehicle for now.
The hull, turret, and some fittings will be modeled when I have the time; note that this is a preliminary sketch, nothing more.

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Alright, at long last I think I have finally finished. Or, at least




I am going to post up some basic data from my worksheets, writeups to follow later.




XM12 Donward Main Battle Tank


Crew: 4

Curb weight: 43.1 t

Gross weight: 45.3 t



100x685R L/52 rifled gun firing APCBC, HE, and APCR

53 rounds capacity, +25/-10 elevation

20x140mm coaxial autocannon firing APHE, HEI, and APDS

7.62mm M240 coaxial machine gun

.50 caliber M2 machine gun

7.62mm coaxial machine gun


Hull armor:

Upper glacis - 4.4" at 28 degrees - 239mm LOS (slightly elliptical)

Lower glacis - 3" at 44.6 degrees - 108mm LOS

Side - 2" at 15 degrees, plus 1"side skirts - 78.4mm LOS (spaced)

Turret armor:

0 degree: 512mm at forehead, 240mm at nose, 186mm above ring

15 degrees: 502mm at forehead, 220mm at nose, 167mm above ring, 339mm sides

30 degrees: 358mm at forehead, 200mm at nose, 147mm above ring, 175mm sides

45 degrees: 262mm at forehead, 154mm at nose, 136mm above ring, 124mm sides



750 hp air-cooled turbocharged V12 diesel, 29.4 L displacement, cross-drive transmission

16.6 hp/t






XM13E4 Sandy Airdroppable Reconnaissance Vehicle


Crew: 3

Curb weight: 12.9 t

Gross weight: 13.9 t



85x640mmR rifled gun firing APCBC, HE, and APCR

34 rounds capacity, +25/-5 elevation

.50 caliber M2 machine gun

7.62mm coaxial machine gun


Hull armor:

Upper glacis - 20mm at 5 degrees, 35mm at 35 degrees (aluminum)

Lower glacis - 35mm at 33.5 degrees (aluminum

Side - 10mm all around (aluminum)


Turret armor

1" thick cupola walls (steel)



305 hp turbocharged water-cooled V6 diesel, 7 L displacement, cross-drive hydrokinetic transmission

22.0 hp/t






XM13E6 Sandy Light Reconnaissance Vehicle


Crew: 4

Curb weight: 17.7 t

Gross weight: 18.6 t



85x640mmR rifled gun firing APCBC, HE, and APCR

34 rounds capacity, +25/-10 elevation (-5 over tracks)

20x140mm coaxial autocannon firing APHE, HEI, and APDS

7.62mm M240 coaxial machine gun

.50 caliber M2 machine gun

7.62mm coaxial machine gun


Hull armor:

Upper glacis - 20mm at 5 degrees, 35mm at 35 degrees (aluminum)

Lower glacis - 35mm at 33.5 degrees (aluminum

Side - 10mm all around (aluminum)

Turret armor:

0 degree: 211mm at base to 248mm at top of gun shield, 244mm at roof

15 degrees: 209mm at base to 245mm at top of gun shield, 241mm at roof

30 degrees: 201mm at base to 238mm at top of gun shield, 234mm at roof

45 degrees: 190mm at base to 226mm at top of gun shield, 221mm at roof

60 degrees: 174mm at base to 210mm at top of gun shield, 205mm at roof



475 hp turbocharged water-cooled V6 diesel, 9 L displacement, cross-drive hydrokinetic transmission

25.5 hp/t






XM15 Roach Medium Tank


Crew: 4

Curb weight: 36.0 t

Gross weight: 37.8 t



100x685R L/52 rifled gun firing APCBC, HE, and APCR

45 rounds capacity, +25/-9 elevation

20x140mm coaxial autocannon firing APHE, HEI, and APDS

7.62mm M240 coaxial machine gun

.50 caliber M2 machine gun

7.62mm coaxial machine gun


Hull armor:

Upper glacis - 55mm at 5 degrees - 631mm LOS

Lower glacis - 125mm at 45 degrees - 177mm LOS

Side - 80mm at 0 degrees


Turret armor:

0 degree: 225mm at base, 225mm at top of gun shield, 225mm at roof

15 degrees: 227mm at base, 212mm at top of gun shield, 217mm at roof

30 degrees: 234mm at base, 197mm at top of gun shield, 211mm at roof

45 degrees: 235mm at base, 191mm at top of gun shield, 198mm at roof

60 degrees: 223mm at base, 187mm at top of gun shield, 191mm at roof



620 hp liquid-cooled V12 diesel, 38 L displacement, cross-drive transmission

16.4 hp/t

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Since I'm in the mood, a little bit of commentary about the process I went through designing these tanks, and, critically, to explain why there are four instead of just two.


Development started with what I always thought of as the "Main Battle Tank" requirement. Given the time period, and since the Baberams/Caracal was an all-welded design that was pretty straightforward to model in SolidWorks, I decided to challenge myself with the Donward and design an all-cast tank. My initial approach to this was satisfactory but... Problematic. I designed the XM12 essentially the same way I had the Baberams, and based many of its features on some of my previous concepts for design competition entrants, as well as the T95 Medium, M103, Chieftain, M48, and Centurion (hence the very "western" look). I emphasized comfort in the design (perhaps a bit too much), and insisted on -10 degrees of gun depression with a 140mm gun, a standing loader, and a centerline driver. Regarding the gun, I wanted to arm it with a rifled gun optimized for APCR ammunition, but knowing that APDS and fin would be on their way before too long I wanted to give the turret as much upgrade potential as possible. The gun I came up with was an 85mm with a round that was initially based on the 7.5cm KwK 42 case, but over time the base expanded slightly to about the same as the 90mm M3. This resulted in the 85x640R which arms the Sandy E4 and E6. To ensure that the Donward would be fully designed for a modern 140mm gun, I made the breech and recoil stroke equivalent to something in that range, and designed the turret around that. As part of an "arms race" between myself and @N-L-M, I developed additional 120mm and 152mm high velocity guns.


To achieve the "cast" look, I ended up extensively using the fillet tool, which created a convincing enough model. However, the model itself was by the end essentially a collection of some hundred and forty-five fillets, which made the model a little unstable and extremely difficult to modify.





^This sucks


This made things much more difficult when, in discussions with @N-L-M it became apparent that while protection was excellent to the point of ludicrous at the 0 degree angle, protection dropped off as the turret turned to the side. Also, the turret had some conspicuous weaker spots near the turret ring that concerned me.


The hull was broadly based on a Centurion, but with an elliptical glacis, since I wanted to figure out how to model one of those. The glacis on the resulting Donward is slightly elliptical, but it probably could have been flat for the same effect. With the hull and turret broadly modeled, I finally decided to take a look at the actual requirements presented in the OP. I discovered that I was barely skating by on width, and that my 50t design weight guideline was five tonnes heavier than the maximum listed in the solicitation. So pro, Nathaniel, so pro. Fortunately, the Donward was a bit under 50t to begin with, and so I was able to reduce the side armor on the hull and make a few optimizations to the turret and bring my curb weight under 45 tonnes. However, the margin I had planned into the design for additional armor and guns was pretty much eaten up by this, which added to my overall dissatisfaction with it.


Despite the issues with the turret and the weight, I wrapped up design of the Donward almost all the way, and moved on to the light tank.


I made some assumptions when designing the Sandy that caused significant difficulty in its design, as well. The first was that I would be able to use the same suspension elements from the Donward and come in under the width limit, and the second was a self-imposed weight limit of ten tonnes. Using a cleft turret and lightweight aluminum construction it seemed like the Sandy would be about 7 tonnes initially, but once all the other elements were added it quickly ballooned to well above 10. This created a dilemma for me regarding the goal of the Sandy, and I explored a handful of other turrets which would bring the Sandy into a class more similar to the T92 or M24. I developed two more heavily armored turrets, one welded one cast. The cast turret was obviously better armored and more lighter, so I decided to continue work with it. Once I began exploring powerplants, however, it became obvious that the idea of turning the Sandy into a "medilite" was not going to work. The Sandy's hull was designed to accommodate a ~300 hp engine, and stuffing in a powerplant that could give a 20 t vehicle more than 20 hp/tonne didn't really seem feasible at the time. It was at this time I decided to redesign the hull.


The first change I decided to make was to change from aluminum to steel, and add armor. Along with that, I moved the engine compartment from the front left alongside the driver to the rear like a normal, sensible tank. I figured that with these changes the tank would come in well over 20 tons and plucked a goal weight of 35 tonnes out of thin air. I figured I would use the elliptical turret I had developed for the new, um, whatever tank. At some point during this process I realized I was basically making a T-55 with more gun depression and decided to embrace this by picking the codename "Roach", however this decision came fairly late to the point that most of the Roach parts and assemblies still reside in the Sandy subfolder. The Roach retained the 5 degree glacis angle of the Sandy, but little else, having essentially a completely new hull, and - eventually - a new turret, too. Shortly after the development of the Roach began, I started to second guess my choice of armament. The 85mm was a potent gun, but its reliance on APCR rather than full caliber shot was something that concerned me. Initially, I bored out the 85mm gun to a 100x640R round, but was quickly caught by the allure of a D-10T analogue. I found that I could do this with a 100x685R round using a wider case base, which resulted in the current 100mm gun that I chose as the final main armament for both the Donward and Roach. Since the Roach was designed for an intermediate 600 hp powerplant, it was quickly converging on the historical T-55.


Upon completion of the first hull assemblies, I discovered that the Roach - like the Sandy - was far too wide to meet the 10.8 foot specification. Discussions with @N-L-M indicated that the Roach's suspension - inherited from the Donward - could use significant optimization. Specifically, I found that the roadwheel arms and spring mount assemblies were designed to properly space against a 20 degree hull angle - while the Roach had sides set at 0 degrees. A program of re-dimensioning and compressing the suspension across the x-axis began, which resulted in a much more compact vehicle in the x-dimension, after which design progressed fairly smoothly. It was this development that proved to be a watershed moment for the Sandy.


The suspension elements developed for the Roach added the promise of finally reigning in the Sandy's always-excessive width. Using these parts, 16" wide tracks (instead of 21" like the Roach and Donward) and with some additional re-dimensioning, the Sandy was finally brought within the 10.8 foot limit, without compromising the already-strapped internal hull volume. It was at this point that I re-married the hull and original cleft turret, and found a reasonable curb weight of less than 13 tonnes - more than I'd wanted at first, but still plausibly air-droppable from an aircraft of the given technology level. The original concept of the Sandy, abandoned days prior, was back.


At the same time, my satisfaction with the Roach's elliptical turret design was low. The turret was a simple construction of a number of revolve and revolve-cut features, which presented some pretty flat angles across the frontal arc, potentially making it more vulnerable to APCR than I'd like. Complex geometry like lofts and boundary features had always been a major problem for me in SolidWorks, but I was going to have to bend them to my will to make a better frying pan turret. After an entire day of struggling with features that didn't want to behave right, I finally ended up with an improved frying pan with the major shape produced though a single boundary feature.





Elliptical turrets, old (top) vs new (bottom). The boundary tool was crucial to producing improved turret geometry.


Comparing the protection of the old and new turrets re-emphasized the poor optimization of the early elliptical design, but this could be fixed fairly easily while making the model simpler, which resulted in a third, "lightweight" design:




The multiple revolve-cuts about different axes of the old turret were replaced with a single carefully dimensioned revolve-cut that produced a continuous transition from the thicker frontal armor to the thinner rear armor, and which didn't leave any thin spots towards the top of the turret, as had been present in the old version. This new version was also some 550kg lighter than the first elliptical turret, which made it a suitable candidate for a new version of the Sandy, which could fill the roll of a sub-20 t light tank for desert campaigns. It was pointed out by @N-L-M that the rubber band tracks of the Sandy would be more resistant to damage from sand and dust than linked metal tracks, provided the weight of the tank didn't exceed a certain threshold. The light version of the elliptical turret would also provide plenty of protection against threats from Deseret, even though its angles were not as extreme as the improved turret. The addition of the 20mm coaxial gun from the Donward and Roach would give the tank plenty of ways to kill light Deseret vehicles, as well. A larger displacement engine equivalent to the DD 6V92T would be a tight fit in the Sandy hull, but would give the tank 25 hp/tonne, which is about what I was shooting for. This version became the XM13E6.


I've skipped over a number of things, such as the numerous variations of cupola and commander's hatch I tried before settling on the current M103-inspired one, and the various armor packages and styles I tried out with the Donward turret, but this should give people some idea of what my process was like.

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On 8/17/2018 at 12:43 AM, LostCosmonaut said:


  • Manufacturing capabilities:
    • The Cascade Republic's ability to cast steel is pretty good; test castings up to ~35 tons and the size of a medium tank hull have been done. Likewise, RHA up to about 6 inches thickness is readily produced. A big limitation is stamping; something like the stamped T-34 turret isn't readily producible (though the cast version is).
    • Plastics are at about early 1950s technology; notably aramids like kevlar and nomex aren't in production (though they are known obviously).
    • Tungsten is available (there are mines in Canada, controlled by friendly nations). DU is not (what can be salvaged from prewar isn't enough for any real use, and gotta have EU to make DU).


What about aluminium, Doron and enamel?

And what about using bolts to make spaced armor?

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Bit of a side issue, but I've been thinking about aluminium matrix composites as armour options for our hypothetical post-post-apocalyptic civilization. This is because they're castable (including differential gradient casting), show good performance against high-velocity projectiles and have great mass efficiency.


The sources I was able to dig up seem to indicate that a confined, optimised Al-AlO MCC might get you a mass equivalence of better than 3 versus RHA. This would be a damn sight better than fused silica fills come the second dawn of improved HEAT rounds and APFSDS.

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From the book "Military Metallurgy", by Alistair Doig:


Aluminium alloy light armoured vehicles (LAV's) first emerged in the early 1950s, being designed with air..transportability and air-droppability in mind for rapid deployment. Not only does the Milne de Marre graph show that aluminium alloy plate at lessthan 75 mm thick gives abetter protection/weight ratio than steel, but its greater bulk means that fewer structural stiffeners are needed and this gives further weight savings. However, these vehiclesonly offer protection against smallarms, rifle- fire, and air-burst HE fragments - they are no match for long rod penetrators and shaped chargewarheads. In the mobility-protection-firepower triumvirate, the accent is very much on the mobility side - these vehicles are supposed to manoeuvre away rapidly from real trouble!

Note that this is a log-log graph, missing a 0 above the 'y' in "heavy"
Unfortunately my source for the book has vanished into the mists of ancient time.

By being lighter, a similar weight of aluminum for a given area is thicker than steel of the same weight. This gives both a better stiffness, resisting bending and buckling, and increases resistance to shear plugging. As can be seen from the graph, above roughly 25mm steel-equivalent, steel starts winning out.

Also note that the definition of "fragment" isn't all that well defined in the graph.A 20mm FSP and a 5.56mm FSP are quite different threats.

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1 hour ago, Collimatrix said:

I was under the impression that aluminum-based armors did really well against artillery fragments and supersonic projectiles, with very good mass efficiency, but once they start dealing with threats in the hydrodynamic velocity range (e.g. APFSDS and HEAT) they were significantly less impressive.

So metal matrix composites are generally where you have ceramics with metals in the place of your polymer binder.


The aluminium MMCs I've seen in literature are 100um-scale SiC or AlO granules mixed with aluminium in a 25-40% ratio. The advantage is that your ceramic is encapsulated and you can, with careful casting methodology, cast the stuff so that the relative proportions of aluminium and ceramic vary across the thickness of the plate. This means, in theory, that you get the best of all worlds by having a ductile back and ceramic-rich front.


Life being what it is this doesn't always work out, which is where encapsulation comes in. In SiC-aluminium MMCs, for instance, the extra silicon you need to add to the aluminium to stop it from forming useless crystal structures means that the whole thing isn't much less brittle than the ceramic alone. So encapsulation has the same positive effects that it would have for any ceramic armour.


Edit: some links




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Anyway, the idea here is that you could cast an aluminium/quartz mix directly into voids ala kvarts and get a cheap-but-effective armour for dealing with HEAT and APFSDS.


Then if you wanted to be really clever you could switch to AlO, adjust the grain size and manage orientation of the piece as you cast to get an MMC with more ceramic at the face and something like a 10% boost in mass effectiveness.

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      Best of luck!
      Update: final submissions should be in hand by the 22nd of November 2020.
    • By SH_MM
      Found a few higher resolution photographs from the recent North Korean military parade. We didn't have a topic for BEST KOREAN armored fighting vehicles, so here it is.
      New main battle tank, Abrams-Armata clone based on Ch'ŏnma turret design (welded, box-shaped turret) and Sŏn'gun hull design (i.e. centerline driver's position). The bolts of the armor on the hull front is finally visible given the increased resolution. It might not be ERA given the lack of lines inbetween. Maybe is a NERA module akin to the MEXAS hull add-on armor for the Leopard 2A5?
      Other details include an APS with four radar panels (the side-mounted radar panels look a lot different - and a lot more real - than the ones mounted at the turret corners) and twelve countermeasures in four banks (two banks à three launchers each at the turret front, two banks à three launchers on the left and right side of the turret). Thermal imagers for gunner and commander, meteorological mast, two laser warning receivers, 115 mm smoothbore gun without thermal sleeve but with muzze reference system, 30 mm grenade launcher on the turret, six smoke grenade dischargers (three at each turret rear corner)

      IMO the layout of the roof-mounted ERA is really odd. Either the armor array covering the left turret cheek is significantly thinner than the armor on the right turret cheek or the roof-mounted ERA overlaps with the armor.

      The first ERA/armor element of the skirt is connected by hinges and can probably swivel to allow better access to the track. There is a cut-out in the slat armor for the engine exhaust. Also note the actual turret ring - very small diameter compared to the outer dimensions of the turret.
      Stryker MGS copy with D-30 field gun clone and mid engine:

      Note there are four crew hatches. Driver (on the left front of the vehicle), commander (on the right front of the vehicle, seat is placed a bit further back), gunner (left side of the gun's overhead mount, next to the gunner's sight) and unknown crew member (right side of gun's overhead mount with 30 mm automatic grenade launcher mounted at the hatch). The vehicle also has a thermal imager and laser rangefinder (gunner's sight is identical to the new tank), but no independent optic for the commander. It also has the same meteorological mast and laser warner receivers as the new MBT.
      What is the purpose of the fourth crew member? He cannot realistically load the gun...
      The vehicle has a small trim vane for swimming, the side armor is made of very thin spaced steel that is bend on multiple spots, so it clearly is not ceramic armor as fitted to the actual Stryker.

      The tank destroyer variant of the same Stryker MGS copy fitted with a Bulsae-3 ATGM launcher.

      Note that there is again a third hatch with 30 mm automatic grenade launcher behind the commander's position. Laser warning receivers and trime vane are again stand-out features. The sighting complex for the Bulsae-3 ATGMs is different with a large circular optic (fitted with cover) probably being a thermal imager and two smaller lenses visible on the very right (as seen from the vehicle's point of view) probably containing a day sight and parts of the guidance system.

      Non line-of-sight ATGM carrier based on the 6x6 local variant of the BTR, again fitted with laser warning receivers and a trim vane. There are only two hatches and two windows, but there is a three men crew inside.
      There are a lot more photos here, but most of them are infantry of missile system (MLRS' and ICBMs).
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