[WWII] Assault Landing Vehicle, Tracked (USA. fictional)

[copeab]

This vehicle came about when I wondered what a WWII version of the BMP-3 would look like and what it would be used for. For those wondering why it's not German, in the campaign the Martians are aiding the Axis and have never had a vehicle remotely like this. The Atlanteans, who are aiding the Allies, have (about 12,000 years ago ...).
-----------------------------------------
ALVT (Assault Landing Vehicle, Tracked)
Copyright 2011 by Brandon Cope

Inspired by Atlantean designs (but using only 1942 Earth technology), the ALVT was intended to provide significant fire support to the first troops to come ashore during an amphibious operation. Rather unusually, it was desiged specifically for the USMC, who normally got rejects or left-overs from the Army and Navy.

The armor was superior to that of the LVT(A) (p.W:DF89) and M-3 halftracks (p.W.109), but poor compared to even light tanks. It did have impressive firepower: a 105mm howitzer to deal with dug-in troops and fortifications, a 20mm cannon to handle vehicles (later replaced with a flamethrower) and three machineguns. Initially it was planned to only carry a nine-man squad but the Marines objected and the vehicle was enlarged to carry a full thirteen-man unit (the larger size actually improved seakeeping, which is still poor).

The ALVT was never intended to replace the cheaper LVT, only to augment it. Each Marine division was equipped with an ALVT battalion of 46 vehicles (with 14 per company and 4 per platoon). When used, they were in the first wave of any major Marine amphibious operations. A total of 329 were operated by the six Marine divisions from January 1943 through the end of the war (including replacements to cover losses and those retired for training).

The vehicle also carries four M-1 carbines, eight fragmentation grenades and four smoke grenades for the crew. Additionally, the bow MG can easily be removed and placed on a tripod if required.

The ALVT-1 has a crew of four. The commander sits in the turret and mans the open-mount A/A machine gun. The gunner and loader/radio operator are split between the turret and body; the gunner fires the howitzer, autocannon and coaxial machinegun. The driver is in the hull, to the left (with the engine and fuel tank to his right) and fires the bow MG (which is in a fixed mount). Thirteen troops are carried and exit either via two roof hatches or a rear drop ramp. The gunner and loader manually traverse the turret at 4.5 degrees per second. The ALVT-1 uses 8.3 gallons per hour at routine usage.

Subassemblies: Waterproofed Immense Tank chassis with mild slope +4, full-rotation Medium AFV turret with mild slope [Body:T] +3, full-rotation Mini Weapon open mount [Tur:T] +0, amphibious tracks +3.
Powertrain: 186-kW diesel engine w/ 186-kW tracked drive train and 54 gallons fuel in self-sealing fuel tank [body]; 8,000-kWs batteries.
Occupancy: 1 CS Body, 2 CS Body/Turret, 1 CS Turret, 13 PS Body Cargo: 2.5 Body.

Armor
Body/Turret: F 5/45, 4/30 other
Tracks: 4/28

Weaponry
105mm Short Howitzer/M-2A1 [Turret:F] (48).
20mm Long Ground AC/M-2 [Turret:F] (450).
Ground LMG/M-1919A4 [Tur:F] (3,000).
Ground LMG/M-1919A4 [Body:F] (2,500).
Very Long Ground HMG/M-2HB [Mini:F] (400).

Equipment
Body: Fire extinguisher, medium radio receiver and transmitter. Turret: 6 smoke dischargers.

Statistics
Size: 25'x12'x9'
Payload: 3.16 tons
Lwt: 17.8 tons
Volume: 178
Maint.: 55 hours
Price: $13,400

HT: 11
HP: 1300 [Body], 112 [Turret], 450 [Each Track], 30 [Open Mount]

gSpeed: 27
gAccel: 4
gDecel: 20
gMR: 0.25
gSR: 6
GP: Very Low (4/5)

wSpeed: 7.5
wAccel: 0.2
wDecel: 10
wMR: 0.1
wSR: 2
Draft: 2.2'

Floatation: 18.8 tons

Design Notes
The cost, weight and HPs of the chassis and turret were divided by two. Track DR was also divided by two.

The 105mm was normally provided with 40 HE and 8 WP shhells. The 20mm autocannon normally used API ammo.

Variants
The Army, in anticipation of the coming invasion of Fortress Europe, ordered 500. The first 100 were the same as the Marine version, to speed delivery. By late 1943 these had been removed from front-line use and were transferred to training units.

The Army was unhappy with several aspects of the design, however, and changes were made to create the ALVT-2 (1944). The next 400 differed in having the diesel engine replaced with two linked 95-kW gasoline engines (as used in the M-3 halftrack). Additionally, the tracks were replaced with a more standard design, giving a speed of 48 mph on land and 4 mph on water (as these vehicles were primarily used on land and for river crossings, this was not a large decrease in capabilities). Finally, and most drastically, the armament was reduced as the Army considered it excessive;.the 105mm howitzer was replaced with a 75mm howitzer (75mm Short TG) with 96 rounds and the 20mm AC was simply removed. Hydraulic traverse (1-kW) was added, good for 13.5 degrees per second. Cargo is 7.5 VSP. Cost was $11,700 and weight 17.6 tons.

Most of the Marine vehicles replaced the 20mm cannon with a more useful flamethrower (Medium Vehicle FT with 15 shots) as the war went along; this was much rarer in those operated by the Army. These were designated ALVT(F)-1 or -2.

There were also some field tests of ALVT-1's replacing the 20mm cannon with a 37mm anti-tank gun. Only a few vehicles were modified and it was not found to be very useful (in particular, it cut into the limited ammo for the howitzer)..

The British received 16 ALVT-1's and 49 ALVT-2's through Lend-Lease. They replaced the 105mm howitzer with a 25 pounder (56 shells) and kept the 20mm cannon. The ALVT-1's were operated in Greece and the ALVT-2's in Burma.

[MEC]

Originally Posted by copeab

This vehicle came about when I wonder what a WWII version of the BMP-3 would look like and what it would be used for. For those wondering why it's not German, in the campaign the Martians are aiding the Axis and have never had a vehicle remotely like this. The Atlanteans, who are aiding the Allies, have (about 12,000 years ago ...).
-----------------------------------------
ALVT (Assault Landing Vehicle, Tracked)
...

Don't know much about the BMP-3, but the allies did have an amphibious assault tank.

http://en.wikipedia.org/wiki/DD_tank

[Dewey]

The Marines did something similar in real life, mounting turrets from the M3 Stuart tank and the M8M-8 on some of their LVTs. I don't know what that did to the carrying capacity though.

[RyanW]

I may be something of a spoil-sport, but it seems odd to arm an IFV with a howitzer. A more practical armament might be a 6 pounder/57mm or 75mm, possibly with one howitzer armed vehicle per platoon or company.

[copeab]

Originally Posted by RyanW

I may be something of a spoil-sport, but it seems odd to arm an IFV with a howitzer. A more practical armament might be a 6 pounder/57mm or 75mm, possibly with one howitzer armed vehicle per platoon or company.

The BMP-3 uses a 100mm low-velocity cannon, so the 105mm howitzer seemed like a good fit. And, since the few Japanese tanks were poorly armored, 105mm HE shells seemed more useful in the Pacific.

I will agree that for Europe an anti-tank gun would be more useful.

[Ulzgoroth]

Originally Posted by copeab

The BMP-3 uses a 100mm low-velocity cannon, so the 105mm howitzer seemed like a good fit. And, since the few Japanese tanks were poorly armored, 105mm HE shells seemed more useful in the Pacific.

I will agree that for Europe an anti-tank gun would be more useful.

Many light post-war vehicles have high-caliber low or medium velocity guns, but they were generally so armed with the intent that they would use HEAT rounds against armored vehicles (or HEAT equipped gun-launched ATGMs).

On the other hand, during the war plenty of armored vehicles were fitted with howitzers and short guns for anti-personnel and anti-bunker use. An IFV that really, seriously is not supposed to fight tanks seems like a reasonable platform for that. Might not want to drive them off the beach (except in the Pacific theater) until you've got some tank-killers ashore as well, though.

[Verjigorm]

Howitzer seems like a better fire support for taking out emplacements and troop formations, which is what you're likely to see on the beach. A machinegun nest that's well hidden might escape naval bombardment, while an enemy tank is likely to be blown the 'eck up by Naval fire.

High Velocity tank cannon are great, but if you're going against Japan... what tanks are you gonna have to shoot at that a 105 won't do justice against? And in europe, what tanks are you gonna shoot at that 57mm AT gun is going to impress it. Maybe the Pzkw4 Js.... who have a 75mm gun and are set up for fighting vehicles. Panthers and tigers are going to mock you as they happily blow you to pieces.

So yeah, I'd prefer a howitzer over an AT gun.

[copeab]

The US did have HEAT rounds for the 75mm and 105mm howitzers, but I'm not sure exactly when they became available.

The BMP-3's main anti-tank weapon is an ATGM fired from the 100mm gun; unfortunately, there is no WWII counterpart* to this, so HEAT rounds would probably have to suffice.

* One remote option is something similar to the German Stielgranate 41, which was essentially a 150mm HEAT rifle grenade fired from their 37mm AT gun. The greatest of it's drawbacks was exposing a crewman to load the grenade over the gun's muzzle.

[Michele]

Originally Posted by copeab

The BMP-3's main anti-tank weapon is an ATGM fired from the 100mm gun; unfortunately, there is no WWII counterpart* to this, so HEAT rounds would probably have to suffice.

* One remote option is something similar to the German Stielgranate 41, which was essentially a 150mm HEAT rifle grenade fired from their 37mm AT gun. The greatest of it's drawbacks was exposing a crewman to load the grenade over the gun's muzzle.

Well, the Germans had the 38cm RW 61. It could fire a purely HE round, or a shaped-charge armor-piercing round (where the armor to be pierced is that of reinforced-concrete fortifications, given the caliber). Both were propelled rounds (rockets). You could fit them with guidance, I suppose, the same used for the X-7 Rotkäppchen, fins, rudder, and IR devices and all. Not particularly necessary for shooting at immobile targets such as bunkers, but if Godzilla, an Elder Thing, or anything else (slowly) moving showed up...

[copeab]

Originally Posted by Michele

Well, the Germans had the 38cm RW 61. It could fire a purely HE round, or a shaped-charge armor-piercing round (where the armor to be pierced is that of reinforced-concrete fortifications, given the caliber). Both were propelled rounds (rockets). You could fit them with guidance, I suppose, the same used for the X-7 Rotkäppchen, fins, rudder, and IR devices and all. Not particularly necessary for shooting at immobile targets such as bunkers, but if Godzilla, an Elder Thing, or anything else (slowly) moving showed up...

The biggest problem is size of the ammo -- a pair of 38cm rockets take up more space than the 48 105mm shells. For every two infantry you dropped you could add only three more rockets.

An existing alternative are the American 7.2" ASW rockets. These were basically a Hedgehog depth charge fitted with a rocket giving it a range of 300 yards and weighing around 85 lbs. They were originally developed as a low-recoil alternative to the Hedgehog for light ships. By 1943 an air-launched version was also available and by 1944 a multi-tube launcher for a demolition version was available (similar to the more famous 4.5" Calliope mounted on some Shermans).

Such rockets would be mounted externally, either in a multi-tube launcher atop to the turret or one or two on rails on each side of the turret (much like the British Sherman Tulip, with two 60-lb rockets).