N-L-M

Clearly, a "paratrooper" variant of the taller infantrymen is needed, so they can be folded for stowage.

Homo Sapiens develops tools to hunt mammoths, Schoningen, 300,000BC [artist's impression]

This is a thread I wanted to post in for a while, and now I'm getting around to it. Spoilered to avoid wall-of-text syndrome.

*weapons-grade naval autism warning*
 
The reason the US carriers are the size they are is pure capability. The 90kton carriers have significantly more capability than their smaller bretheren, for a few reasons.
There are a few notes I want to address on this point.
1. Deck size
 

 
2. Survivability
 

3. Force concentration
 

4. Why then, if big is so good, aren't they larger?

5.  Are carriers the future? 
 
There is more to say, and I may have a follow-up post at some point.

This is a thread I wanted to post in for a while, and now I'm getting around to it. Spoilered to avoid wall-of-text syndrome.

*weapons-grade naval autism warning*
 
The reason the US carriers are the size they are is pure capability. The 90kton carriers have significantly more capability than their smaller bretheren, for a few reasons.
There are a few notes I want to address on this point.
1. Deck size
 

 
2. Survivability
 

3. Force concentration
 

4. Why then, if big is so good, aren't they larger?

5.  Are carriers the future? 
 
There is more to say, and I may have a follow-up post at some point.

This is a thread I wanted to post in for a while, and now I'm getting around to it. Spoilered to avoid wall-of-text syndrome.

*weapons-grade naval autism warning*
 
The reason the US carriers are the size they are is pure capability. The 90kton carriers have significantly more capability than their smaller bretheren, for a few reasons.
There are a few notes I want to address on this point.
1. Deck size
 

 
2. Survivability
 

3. Force concentration
 

4. Why then, if big is so good, aren't they larger?

5.  Are carriers the future? 
 
There is more to say, and I may have a follow-up post at some point.

This is a thread I wanted to post in for a while, and now I'm getting around to it. Spoilered to avoid wall-of-text syndrome.

*weapons-grade naval autism warning*
 
The reason the US carriers are the size they are is pure capability. The 90kton carriers have significantly more capability than their smaller bretheren, for a few reasons.
There are a few notes I want to address on this point.
1. Deck size
 

 
2. Survivability
 

3. Force concentration
 

4. Why then, if big is so good, aren't they larger?

5.  Are carriers the future? 
 
There is more to say, and I may have a follow-up post at some point.

This is a thread I wanted to post in for a while, and now I'm getting around to it. Spoilered to avoid wall-of-text syndrome.

*weapons-grade naval autism warning*
 
The reason the US carriers are the size they are is pure capability. The 90kton carriers have significantly more capability than their smaller bretheren, for a few reasons.
There are a few notes I want to address on this point.
1. Deck size
 

 
2. Survivability
 

3. Force concentration
 

4. Why then, if big is so good, aren't they larger?

5.  Are carriers the future? 
 
There is more to say, and I may have a follow-up post at some point.

This is a thread I wanted to post in for a while, and now I'm getting around to it. Spoilered to avoid wall-of-text syndrome.

*weapons-grade naval autism warning*
 
The reason the US carriers are the size they are is pure capability. The 90kton carriers have significantly more capability than their smaller bretheren, for a few reasons.
There are a few notes I want to address on this point.
1. Deck size
 

 
2. Survivability
 

3. Force concentration
 

4. Why then, if big is so good, aren't they larger?

5.  Are carriers the future? 
 
There is more to say, and I may have a follow-up post at some point.

Clearly, a "paratrooper" variant of the taller infantrymen is needed, so they can be folded for stowage.

This is a thread I wanted to post in for a while, and now I'm getting around to it. Spoilered to avoid wall-of-text syndrome.

*weapons-grade naval autism warning*
 
The reason the US carriers are the size they are is pure capability. The 90kton carriers have significantly more capability than their smaller bretheren, for a few reasons.
There are a few notes I want to address on this point.
1. Deck size
 

 
2. Survivability
 

3. Force concentration
 

4. Why then, if big is so good, aren't they larger?

5.  Are carriers the future? 
 
There is more to say, and I may have a follow-up post at some point.

Loader's position:

Turret details are now in.

The turret and hull were slightly enlarged to improve ergonomics, the tank looks a bit strange now.
The depicted optics are a bit of a "how much optic can I stuff in here anyway" sort of deal, I'm not sure it's even possible to make the rangefinder in the cupola work. But the idea is that when IR optics become a thing they can be seamlessly integrated. Also the gunner's line of sight is stabilized in elevation (by the magic of mirrors and electric servos), the gun drive (hydraulic) is slaved to follow it. This allows good LoS stabilization, and firing on the move can be regulated by the difference between LoS and gun (MG only, main gun from short stop).
Next up on the agenda:
-Sideskirts
-Hull armor improvements
-Sponson goodies
-driver's hatch
-hull interior details.
It may however be a while until my next post.

Turret details are now in.

The turret and hull were slightly enlarged to improve ergonomics, the tank looks a bit strange now.
The depicted optics are a bit of a "how much optic can I stuff in here anyway" sort of deal, I'm not sure it's even possible to make the rangefinder in the cupola work. But the idea is that when IR optics become a thing they can be seamlessly integrated. Also the gunner's line of sight is stabilized in elevation (by the magic of mirrors and electric servos), the gun drive (hydraulic) is slaved to follow it. This allows good LoS stabilization, and firing on the move can be regulated by the difference between LoS and gun (MG only, main gun from short stop).
Next up on the agenda:
-Sideskirts
-Hull armor improvements
-Sponson goodies
-driver's hatch
-hull interior details.
It may however be a while until my next post.

Turret details are now in.

The turret and hull were slightly enlarged to improve ergonomics, the tank looks a bit strange now.
The depicted optics are a bit of a "how much optic can I stuff in here anyway" sort of deal, I'm not sure it's even possible to make the rangefinder in the cupola work. But the idea is that when IR optics become a thing they can be seamlessly integrated. Also the gunner's line of sight is stabilized in elevation (by the magic of mirrors and electric servos), the gun drive (hydraulic) is slaved to follow it. This allows good LoS stabilization, and firing on the move can be regulated by the difference between LoS and gun (MG only, main gun from short stop).
Next up on the agenda:
-Sideskirts
-Hull armor improvements
-Sponson goodies
-driver's hatch
-hull interior details.
It may however be a while until my next post.

Turret details are now in.

The turret and hull were slightly enlarged to improve ergonomics, the tank looks a bit strange now.
The depicted optics are a bit of a "how much optic can I stuff in here anyway" sort of deal, I'm not sure it's even possible to make the rangefinder in the cupola work. But the idea is that when IR optics become a thing they can be seamlessly integrated. Also the gunner's line of sight is stabilized in elevation (by the magic of mirrors and electric servos), the gun drive (hydraulic) is slaved to follow it. This allows good LoS stabilization, and firing on the move can be regulated by the difference between LoS and gun (MG only, main gun from short stop).
Next up on the agenda:
-Sideskirts
-Hull armor improvements
-Sponson goodies
-driver's hatch
-hull interior details.
It may however be a while until my next post.

Thanks to @N-L-M I now have some reasonably convincing suspension elements:
 

I now have a basic suspension, Merkava-3 style (the springs aren't modeled yet). If anyone has a quick easy way to make a drive sprocket I'd love to hear it.
Also the surfaces left in the rough from casting now look the part.

The gun clears the sponson corners:

If anyone's wondering, those are M60 wheels cut down in width by about an inch.

The tank boasts a low-profile silhouette in hull-down positions:
 

I am suddenly very sure that the M240 model I am using is about two times bigger than it should be...
 

@LostCosmonaut, here's a what I came up with:
 
Light Tank M6
 

 
Basic statistics
Length: 5.08m, 5.18m (total) Width: 1.65m (hull), 2.6m (total) Height: 2.48m (40cm ground clearance) Weight: 11 t (combat weight) Crew: 4 (commander, gunner, driver, radio operator) Armour
25mm (upper hull front) 25mm (lower hull front) 25mm (hull side forward) 10mm (hull side rear) 10mm (hull rear) 10mm (hull roof) 15mm (hull floor) 25mm (turret front) 25mm (turret front side) 15mm (turret rear side) 15mm (turret rear) 10mm (turret roof) Weapons
40mm L/50 cannon (movement: -15/+30 degrees vertical), 100 rounds stowed                       APHE: 0.85kg, 790m/s, ~40mm penetration against RHA (500m, 90')
                      AP: 1.22kg, 790m/s,  ~50mm penetration against RHA (500m, 90')
M240 machine gun (coaxial), 1600 rounds stowed M2 heavy machine gun (turret roof), 1200 rounds stowed Drivetrain
Engine: 5L, 150 HP (112 kW) V8 petrol engine (Chevy small block derivative, because if there's one thing post-apocalyptic Americans will be able to make it's a small-block V8) Power/weight:  9kW/t Max speed (road): 50km/h Max sustained speed (offroad): 30km/h Range: 500km

 
Notes
The 40mm gun is essentially a 2 Pounder with access to solid AP, HE and canister (for scrubbing survivalists and tribals off your mate's vehicle). A 55mm gun can be fitted, although it's awkward (as in, the breech is 20cm from hitting the turret ring at certain elevations). The vertical movement is also more restricted (-10/+20 degrees). The hull is mostly welded while the turret, hatches and rear transmission housing are cast. The turret ring diameter is 125cm. The turret drive is manual, but I'd guess that later models include a powered drive of some sort. The weird front hatch design is intended to include a pivot point and hinge. The hull crew is supposed to be able to flip up the hatch for better (but still protected) vision. The transmission would be Cletrac-derived. So don't expect neutral steering. My suggested name for it is 'Fox'. Mainly because this gives the troops plenty of scope for more entertaining nicknames (an older commander's vehicle is a 'Silver Fox', a female commander's is a 'Cougar' and so on). It turns out to be quite a challenge to design something that looks functional but a bit primitive without it looking seriously goofy.

 
Acknowledgements: 
bAtsi robboposh .. Share link: https://drive.google.com/open?id=1dANQNANroc36WrI_hFOZT-Wt_ZDkhgGb
 
 

Still working in 3ds max for now since I feel it's better for just roughing out ideas, but pooped out something just as a sort of warmup.  Dunno if I'll keep it or not, but it'd be a light tank of some sort.

On the other hand: design-a-firearm competition entrants in the 1980s would be very surprised to see their field dominated in TYOOL 2018 by derivatives of late-50s and early-70s designs.

Clearly, a "paratrooper" variant of the taller infantrymen is needed, so they can be folded for stowage.

SPG and SPAAG variants:
 
XM9 “Black Bear”
 

Basic statistics
Length: 6.6m (hull), 11.4m (total) Width: 2.65m (hull), 3.25m (total) Height: 2.5m Weight: 48 t (combat weight) Crew: 4 (commander, gunner, loader, driver) Armour
100mm (upper hull front) 100mm (lower hull front) 65mm (hull side forward) 25mm (hull side rear) 25mm (hull rear) 25mm (hull roof) 25mm (hull floor) 100mm (mantlet) Weapons
 
120mm L/50 cannon:
APHE: 23.9kg, 875m/s, ~200mm RHA penetration (90’, 500m) APCR: 13.6kg, 1045m/s, ~300mm RHA penetration (90’, 500m) HE: 21.7 kg, 500m/s Movement: +/- 12 degrees horizontal, -10 degrees/+30 degrees vertical Browning M2 heavy machine gun (hull roof)
 
Drivetrain
Engine: 18L, 500 HP (373 kW) V8 petrol engine (Ford GAA derivative) Power/weight:  10.4kW/t Max speed (road): 35km/h Max sustained speed (offroad): 25km/h Range: 300km Description
 

Sometimes you just need whatever is in front of your position to die. The M9 “Black bear” is designed to make everything in within range of its gun go away as efficiently as possible. Armed with a long 120mm gun (a calibre with special significance to Cascadians thanks to its storied history), this SPG is capable of punishing any presently fielded armoured vehicle out to long ranges with standard APHE. APCR, although not presently required, has also been developed in order to deal with any superheavy vehicles which may be developed in the near future. Finally, the gun has access to a very useful low-velocity HE round, along with more specialised rounds such as smoke and star shells.
 
The M9 is a casemate tank destroyer, with a 50cm superstructure on top of the hull to help accommodate the massive gun. The result is a vehicle is not much shorter than the tank it is based on. In terms of protection; the much higher slope of the upper front plate (60 degrees versus 45 degrees for the M8) provides a significant increase in survivability against threats from the front. Otherwise, the armour is the same as the base vehicle.
 
The superstructure and front plate, when combined with the massive gun, did unfortunately result in a significant increase in weight over the M8. As a result the front suspension needed to be strengthened and a new transmission system needed to be designed for the extra load. The latter was probably a good idea in any case, as this allowed neutral steering to be included in order to assist the gunner. The horizontal and vertical travel of the gun is about average for this sort of vehicle, and is adequate for the task at hand.
 
The interior of the crew compartment is relatively roomy, which is helpful given the increased burden on the loader. The main gun uses two-piece ammunition, which lowers the overall rate of fire somewhat but allows one man to load the main gun. Crew comfort is also increased thanks to a forced-air bore scavenging system, which significantly cuts down on smoke and fume buildup inside the vehicle.
 
Overall; the M9 is expected to serve in limited numbers compared to the M8, but should provide a very useful capability for engaging in defensive operations against heavy armour or offensive operations against fixed fortifications.
 
XM10 “Goshawk”
 

Basic statistics
Length: 6.6m Width: 2.65m (hull), 3.25m (total) Height: 2.8m Weight: 20 t (combat weight) Crew: 3 (commander, gunner, driver) Armour
25mm (upper hull front) 25mm (lower hull front) 25mm (hull side forward) 15mm (hull side rear) 15mm (hull rear) 15mm (hull roof) 15mm (hull floor) 25mm (turret front) 25mm (turret front side) 15mm (turret rear side) 15mm (turret rear) 15mm (turret roof) Weapons
2x20mm autocannon (movement: -10/+80 degrees vertical) Drivetrain
Engine: 18L, 450 HP (340 kW) V8 petrol engine (Ford GAA derivative) Power/weight:  22.5kW/t Max speed (road): 45km/h Max sustained speed (offroad): 35km/h Range: 500km Description
 

The M10 is simply a light version of the M8 with an open-topped turret designed to hold two 20mm autocannon. The mount is based on the venerable ZSU-23-2 design, and has good movement in the vertical. The electric turret drive can push the turret through a full rotation in around 10 seconds, which assists in tracking fast-moving targets.
 
The M10 is expected to be useful when dealing with low-flying aircraft and infantry, and should fill a useful niche within the armoured force.

Clearly, a "paratrooper" variant of the taller infantrymen is needed, so they can be folded for stowage.

Right, I think I have a pretty good idea of what the basic turret will look like. The front and cheek armor and ring are cast, the flanks, rear, roof, and under bustle are rolled.

Structure estimated at 5.7 tons, not bad for an initial design. Combined with the hull being slimmed down to 13.3 tons, I get 19 tons so far. Assuming a ~50% armor weight fraction, that leads me towards 40 tons, which is a good place to be.
I should probably stop for the day.
EDIT: ballistic fixes bring me to 5.8 on the turret.
To prevent multiposting:
It seems I got my sizes a bit off, the turret is a bit too small for the hull.