MBT-70

The MBT-70 was a 1960s joint German -U.S.-project to develop a new main battle tank using a number of advanced design features. It used a kneeling suspension, housed the entire crew in the turret, and the American version incorporated a gun-fired missile.

By the late 1960s the project was well over budget and the Germans withdrew from the effort, developing their Leopard 2 instead. Development continued in the US, but the per-unit cost had risen five times, and in 1971 Congress overrode the Army's objections and the MBT-70's funding was redirected to create the more successful M1 Abrams.

Development
In the early 1960s, it became clear that the USSR was planning to introduce a successor to their T-62 and T-55/54 designs, one with an auto-loading gun and better armor, which was eventually delivered as the T-64 and the cheaper T-72. The new design would place the US's existing M60 tanks at a disadvantage, so the U.S. Army started looking at designs that would surpass any potential Soviet design. The Germans faced the same problem; the recently introduced Leopard 1 tanks were on the verge of becoming obsolete after only a few years. An upgrade project for the Leopard was already underway, but it appeared this model would not be enough of an advance to be worthwhile.

The result was a joint agreement to develop a single new tank for both armies. However, this may have been one of the worst things to happen to the project, as both teams started "pulling" the design in their own directions. Arguments arose over almost every part of the design: the gun, the engine, even whether or not the design would use metric or SAE measurements. This last dispute was eventually "settled" by using both systems, thereby increasing costs considerably.

Many features of the MBT-70 were ahead of their time. The vehicle used an advanced hydropneumatic suspension system that allowed for fast cross-country speeds even though it was to weigh 50 ST. The suspension could be raised or lowered on command by the driver, down to put the bottom of the tank just over 4 in from the ground, or up to 28 in for cross-country running.

The armor consisted of two spaced layers, the inner a softer steel that also served as a spall liner, and the outer of harder cold-rolled steel. The spacing was included to help defeat HEAT rounds, notably those on wire guided missiles, then one of the most dangerous weapons deployed against tanks. The design included bulkheads, fireproof doors, and blow-out sections in the ammunition storage area to minimize crew injury when a hit was received.

The MBT-70 was designed with a low silhouette (low height), something which had not been addressed on the M60 whose high silhouette was considered a serious drawback. In fact, the MBT-70 ended up so low, just over 6 ft from the floor to the top of the turret, that there was no room for the driver in the main hull. Instead he was placed with the rest of the crew in the seemingly oversized turret, in a contrarotating cupola that was geared to keep him facing forward. If needed, the cupola could be turned around to face to the rear, allowing the tank to be driven backwards at full speed.

US versions were to mount the new Continental AVCR air-cooled V-12 diesel of 1470 hp. German versions originally used a similar Daimler-Benz model, but later moved to an MTU design of 1500 hp. The MTU unit could be easily swapped out of the tank, along with the drive train, in 15 minutes. Both versions could reach 43 mph on their engines, at the time an unheard-of speed for such a large tank.

The US version was armed with the new XM-150 auto-loading stabilized 152 mm gun/launcher system equipped with a laser rangefinder, then a cutting edge device. The gun was a medium-velocity design that fired artillery-sized high explosive shells in the anti-personnel role, and used HEAT rounds for short-range armored threats. For long-range anti-tank firing the gun could be loaded with the Shillelagh missile. The result was a light gun with the same firepower as a much larger "standard" design. The Germans were suspect of this design and instead planned to equip their versions with their newly-developed Rheinmetall 120 mm gun, also equipped with an auto-loader. Secondary armament for both consisted of a remote-controlled 20 mm cannon that popped up from a hatch behind the driver's cupola for anti-aircraft use, a 7.62 mm machine gun mounted coaxially alongside the main gun, and smoke dischargers on either side of the rear turret. The use of an auto-loader for both versions allowed the crew to be reduced to three: commander, gunner and driver.

Testing
A prototype series started in 1965, with one mild steel hull and six "complete" hulls of both the US and German versions, for a total of 14 hulls. The lower hull and drivetrain were tested in 1966, and full trials began in 1968.

The tank proved to be better than the M60: it was considerably faster, both in all-out speed and, more importantly, with about three times the acceleration. In cross-country performance the high power engine and excellent suspension allowed it to travel almost three times as fast as the M60 without causing problems for the crew. All of this led to a reduction in the time the tank was exposed to fire, in testing it was 1/3rd less likely to be seen while maneuvering than the M60, and it could run a 10 km (6 mile) obstacle course in 30 % less time.

Problems
A problem that was not anticipated was that the drivers complained of disorientation when the turret was rotated, contrary to the predictions of the designers who felt the location of the cupola near the center of rotation would eliminate this effect. The German 120 mm proved excellent, but the XM-150 was a serious problem. The similar but smaller XM-81 mounted on the M551 Sheridan proved to be just as troublesome. The American version had additional problems with ammunition. The XM-150 was initially designed to use prototype caseless ammunition as part of the American push for the use of caseless ammo as standardized NATO ammunition. As is often a problem with caseless ammo, XM-150 ammunition had a tendency to "cook-off," or fire prematurely, due to heat build-up in the barrel from previously fired rounds. The attempted solution, to only carry a single round with the balance in missiles, also proved unacceptable. Deployment of the 20mm anti-aircraft cannon also proved difficult and the weapon itself was overly complicated and nearly impossible to use effectively. Commentators on the MBT-70 typically assert that though it was innovative in many respects, the project was ruined by the use of too many untried and unproven technologies.

Cancellation
By 1969 the MBT-70 cost five times what was projected, at $1 million a unit ($ in present-day terms). Germany backed out of the project, and re-started development of what would become the Leopard 2. At this point Congress also began objecting to the rapidly increasing price and soon canceled it in 1970. The Army then introducing a lower-cost system based on the same design, known as the XM803. This succeeded only in producing an expensive system with capabilities similar to the M60 it was supposed to replace.

Congress, angered by the delays and cost overruns, cancelled the project in November 1971, and redistributed the funds to the new XM815. This project was later renamed XM1, the project that led to the very successful M1 Abrams tank. The M1 had a conventional turret, suspension, and gun, but would be innovative in incorporating advanced armor materials and the use of a gas turbine engine.