The 120mm gun tank T110 was a series of designs for a heavy tank armed with a hull mounted main gun, developed as an alternative to the Heavy Tank T43 and its long term replacements.
The T110 emerged from the Question Mark III conference of June 1954, one of a series of meeting between tank users and designers that were meant to identify the type of tanks that would be needed in the future. Six possible designs for heavy tanks were discussed at this conference - four short term projects and two long term projects.
One of the short term projects was for the TS-31. This would carry a 120mm gun T123E1 in a gimbal mount with a limited traverse, carried in the front of the vehicle's superstructure. Models and drawings show a five man vehicle with the driver in the nose (below the gun barrel) and the gunner, loaders and commander in a fighting compartment in the middle of the tank. It would have five large road wheels and a flat track suspension system, in which the return run of the track ran along the top of the large road wheels.
The TS-31 was elected for further development, for use either as an assault model, or as a backup in case the Heavy Tank T43E2 or the long term TL-4/ 105mm gun tank T96 failed. Chrysler was given the contract to development the T110.
The first design was provided by the Detroit Arsenal. The superstructure had a curved front and sloped sides. The commander's cupola was on the front-right of the fighting compartment, and would be topped by a fully rotating machine gun turret. Power was to be provided by a Continental AV-1790 engine carried at the back of the vehicle, and powering an XTG-500 transmission in the front of the vehicle. It was to be armed with a 120mm gun T123E1 in a rigid mount - this eliminated the complex recoil mechanisms used in existing tanks, and used the weight of the vehicle to absorb the recoil forces.
The main problem with this design was that it was too large for the standard European railway loading gauge, agreed at a conference in Berne, Switzerland, in 1912 and that went into force in 1914. This specified a width of 10ft 4in, a height of 10ft 5in at the sides and of 14ft 1in in the centre. Some sources refer to this as the 'Berne International Tunnel', but in fact it relates to all aspects of railways, including bridges and station platforms.
Chrysler came up with a series of alternative designs. In their first design the cab was reduced in width and the commander was moved to the centre-rear. This meant that his cupola would fit under the high point at the centre of the Berne standard. The drive was moved from the hull front to the cabin front. The drive was on the front right, with the gunner on the front left. The loaders were on either side of the breech, and the commander was behind and above the. The number of road wheels rose to five. The tracks and cupola periscope would both have to be removed for rail transport. The new driver's position allowed the nose to be used to store fuel, and made the controls easier to link to the transmission.
The Detroit Arsenal objected to the new layout. Chrysler produced a second design, with the driver back in the hull front, on the front left. The gunner moved to the front left of the cab. The loaders and commander remained in their existing positions. The nose was shortened to improve its ability to cross obstacles, and the front idlers and road wheels adjusted. The fuel storage had to be removed from the hull front.
The Detroit Arsenal then produced a new basic design. This time the transmission was moved to the rear. The commander's cupola was moved to the right, meaning that the entire thing would have had to be removed for railway clearance. The flat track suspension was to be replaced with a more conventional type with return rollers. A new Continental AOI-1490 air-cooled fuel injected engine, capable of providing 700hp at 2,800rpm was specified. A large fuel tank was located in the nose, to the front and right of the driver.
Chrysler produced a third design in response to the Arsenal's second design. This soon ran into problems. The engine and transmission would be below and to the left of the commander, and would have been difficult to maintain. In an attempt to solve this problem they were placed on rails, and could slide out of the vehicle through a rear hatch. This weakened the vehicle and made it hard to keep the transmission lined up with the final drive. It also reduced the amount of space available for cooling grills.
Chrysler came up with a four design, which solved the engine problems and also reduced the height of the vehicle enough to make sure that only the tracks would have had to be removed for railway clearance. The fighting compartment was moved forward and the rear of the tank was lengthened. The engine and transmission could thus be installed into a more conventional engine compartment, with a flat roof behind and below the back of the fighting compartment. The exhaust gases could be mixed with cool air to try and reduce the infrared signature of the vehicle. The transmission and cooling problems would thus be eliminated. The crew reverted to similar positions to Chrysler's first design, with all five in the superstructure. This time the driver was on the front right and the gunner on the front left. The loaders were behind them, and the commander was above and between the loaders. The 120mm gun was mounted behind a 9in thick two ton gun shield, and has a traverse of 15 degrees on either side and an elevation range of +20 to -10 degrees. The gunner's seat would have moved with the gun. The driver would have been rather squeezed into a corner when the gun was traversed fully to the left (when the section inside the mount would have swung right). There would be six large road wheels, and a raised front idler and rear drive wheel. A pulsed light range finder would have been installed in the cupola.
By this point Chrysler was no longer convinced that the superstructure mounted gun offered any advantages. Their fifth design was thus for a far more conventional assault tank, carrying the same 120mm gun in a fully rotating turret. Their design drawings show a vehicle that kept much of the basic hull of the fourth design, including the suspension system and the engine and transmission system and rear drive wheel. The superstructure was eliminated and a large turret on the 85in turret ring used on the Heavy Tank M103 was installed instead. The driver returned to the front of the hull. The driver and commander sat to the left of the gun, the single loader on the right. A power rammer was added to make up for the removal of the second loader. This design was expected to weight less than the 50 ton limit for the T110, it would use standard tank components, and the turret made it more flexible than the limited traverse of the earlier designs.
A full scale model of this fifth design was actually built at the Detroit Arsenal, but by now interest in the T110 was fading. The Heavy Tank T43E2 project had been successful, but at the same time the heavy tank was going out of favour. Future projects would carry heavy guns on lighter vehicles than the T110.