[Would you like to see this in-game?]
TL;DR: An M1A2 Abrams mounted with the M256E1 L/55 120mm cannon.
Development of the Rh-120 L/55 120mm gun began in 1991 when Germany, Switzerland, and the Netherlands agreed to cooperate in the development of a modernized Leopard 2. This modernization project included a lengthened 120mm gun, which was much cheaper than a the development of an entirely new cannon. The resulting weapon was the Rh-120 L/55. As their M256 120mm cannon was heavily based on the Rh-120 L/44, you can be sure that the US followed the development of the new L/55 variant very intently. From 1998 to 2000, the US tested three modified Rh-120 L/55s, as well as an additional twelve barrels produced under license by TACOM/Watervliet Arsenal, under the designation of M256E1. At least one of these guns was mounted onto an M1A2 Abrams. Problems immediately arose. You see, the Rh-120 L/55 was developed specifically to suit the Leopard 2’s gun mount. The 120mm armed Abrams tanks featured a gun mount and stabilization systems that differed from the Leopard 2s’. It was quickly discovered that these systems were far too weak to properly handle the longer and heavier M256E1. This effectively meant that the M1A2, in this configuration, was not fully stabilized, making firing accurately on the move very difficult if not impossible. Fixing this issue meant an entirely new stabilization system needed to be developed alongside other necessary major modifications. It was deemed that the cost of this would not be worth the performance increase and the project was dropped.
Place In War Thunder:
What we have here is effectively an unstabilized M1A2. Yes, the gun might perform very well, however, that doesn’t matter if you can’t get it on target. Coming to a sudden stop in this thing would result in massive gun-wobbles. By the time you manage to get the gun on target, you’d have already been shot twice. It’s likely that the elevation mechanism would be more fragile as well. Even as low as 9.7, these problems would make the vehicle a challenge to play even with the M1A2’s armor. You’d have to resign to a sniping role where you can make use of your weapon without having to engage while moving. Personally, I believe that a vehicle like this would be perfect example of how to do a high-tier squadron vehicle correctly. The Leopard 2PL is just as effective as the Leopard 2A5. This isn’t good. It essentially allows you to buy a very effective top-tier vehicle even if you’re a new player. The M1A2 M256E1, on the other hand, is just an overall worse version of a tank that is available in the tech tree. It does not exceed the standard M1A2 in any way except for firepower, but to get this firepower it traded away one of its most necessary systems.
Armament: M256E1 L/55 120mm cannon, 1x 12.7mm machine gun (maybe), 1-2x 7.62mm machine gun
Dimensions: 7.93m, 3.66m, 2.44m (L,W,H)
Armor: Same as M1A2 in-game (Most likely)
Crew: 4 (Commander, Driver, Gunner, Loader)
Ammunition: Exact ammunition unknown, however, I assume it could fire all standard US 120mm ammunition.
Below The Turret Ring: Upgraded Abrams to feautre XM360 gun and guided ammunition?
M256 120mm Smoothbore Gun