In the early 1960s the German Leopard 1 and the US M60 were the newest main battle tanks in their respective country's service. While designed to counter the T-54/55 tanks, it became clear that the next generation of Soviet tanks would have increased firepower and protection, and both designs would be placed at a disadvantage by the new smoothbore gun in the T-62. An upgrade project for the Leopard was planned, but it appeared this model would not be enough of an advance to be worthwhile.
In order to develop a vehicle that would meet the standards of both armies, Germany and the United States drafted a memorandum of understanding that specified certain desired characteristics and organized a Joint Engineering Agency and a Join Design Team with equal representation from both countries. Despite these measures, conflicts between the differing engineering practices of each country plagued the MBT-70 project throughout its development. Arguments arose over almost every part of the design: the gun, the engine, and the use of both metric and SAE units in the separately-manufactured components of the tank. While this last dispute was settled by an agreement to use a common metric standard in all interface connections, the resulting complexity contributed to delays in the development schedule and the ultimately inflated budget of the project.
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 45 tonnes (50 short tons). The suspension could be raised or lowered on command by the driver, down to put the bottom of the tank just over 4 inches (100 mm) from the ground, or up to 28 inches (710 mm) for cross-country running.
The MBT-70 was designed with a low silhouette, unlike the M60, one of the tallest tanks ever built. The MBT-70 ended up very low, just over 6 feet (1.8 m) from the floor to the turret-roof. This left no room in the hull for the driver, who had to be moved into the turret. He was located in a cupola which was geared to rotate so that he was always looking in the same direction even if the turret turned. He could also spin the cupola around, so the tank could be driven backwards at full speed.
The US version was to mount the newly developed Continental AVCR air-cooled V-12 diesel of 1,470 horsepower (1,100 kW). German versions originally used a similar Daimler-Benz model, but later moved to an MTU design of 1,500 horsepower (1,100 kW). The MTU unit could be easily swapped out of the tank, along with the drive train, in 15 minutes. Both versions could reach 43 miles per hour (69 km/h) on their engines, compared to 30 miles per hour (48 km/h) for the T-62.
The MBT-70's main armament was a stabilized XM150 152 mm gun/launcher, a longer-barreled and improved variant of the XM-81 gun/launcher used in the light M551 Sheridan and the M60A2 "Starship". This gun/launcher could fire conventional 152 mm rounds like High Explosive, anti-personnel, High Explosive Anti-Tank (HEAT) and Armor Piercing Fin-Stabilized Discarding Sabot (APFSDS) rounds, but also the Shillelagh missile, a 152 mm guided missile, which had a combat range of some 3,000 metres (9,800 ft). In the 1960s the effective combat range of the 105 mm L7 tank gun was considered to be about 1,800 metres (5,900 ft). The XM578 APFSDS round was made of a newly developed tungsten alloy, which was 97.5 percent tungsten. This new alloy had a density of 18.5 g·cm³, which was a big improvement compared to the older tungsten-carbide APDS and APFSDS rounds. Another new feature of the ammunition was that the tank rounds were "caseless"; i.e., they had combustible cases.
The MBT-70 was equipped with a laser rangefinder and an auto-loader, located in the turret rear, two 'cutting edge' devices for this time. The auto-loader was capable of loading both missiles and normal tank rounds.
The Germans were planning to use the MBT-70 in combination with the Keiler, a tank equipped with a Rheinmetall 120mm smoothbore gun. Therefore, a suggestion was made to base a version of the Keiler on the MBT-70 chassis — this version was nicknamed Eber, but only a wooden mock-up was made. According to the German plans, the MBT-70 would destroy enemies at long ranges, while the Keiler would have an effective combat range of up to 2,000 metres (6,600 ft).
The secondary armament of the MBT-70 consisted of a remote-controlled 20 mm Rh 202 autocannon for use against aircraft and light armoured vehicles. The gun could be retracted into a container behind the driver's rotating cupola for protection as well as to reduce overall height, and was operated remotely by the commander. Furthermore, a 7.62 mm machine gun was mounted coaxially alongside the main gun for close-defense. The US prototypes were fitted with the M73 machine gun, while the German version utilized the MG-3 machine gun.
The ammunition load of the MBT-70 prototype seen in the Deutsches Panzermuseum consists of 42 tank rounds, 6 Shillelagh missiles, 660 20×139 mm cannon rounds and 2,700 7.62×51mm NATO machine gun rounds.
The MBT-70 was protected by a newly developed type of spaced armor in the frontal area of the hull and the turret. It consisted of an outer layer made of cold-rolled hardened steel and a softer inner steel layer, which also served as spall liner with space between the two. This type of armour offered better protection against armor-piercing and HEAT warheads, which were by then one of the strongest threats against tanks. The armor offered protection against 105 mm APDS at a range of only 800 metres (2,600 ft).
The tank's low silhouette, which could be lowered from 2.59 metres (8 ft 6 in) to only 1.99 metres (6 ft 6 in), was also a big advantage. Compared to the M60 tank, the MBT-70 had a lower profile. With the hydropneumatic suspension lowered it was also smaller than the Leopard 1, which gave the MBT-70 a better hull down position.
For protection against neutron radiation a 15 to 20 cm thick layer of polythene was installed around the crew compartment. The MBT-70 was protected against electromagnetic pulses and nuclear, biological and chemical weapons as well.
The MBT-70 was capable of reaching a top speed of 43 miles per hour (69 km/h), and maintained a higher level of mobility than any tank of its time. It was considerably faster than the M60 and even faster than the Leopard 1 tank. It also could accelerate three times faster than the M60. In cross-country performance the high power engine and hydropneumatic suspension allowed it to travel almost three times as fast as the M60 without causing problems for the crew.
A prototype series started in 1965, with two 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. All of this led to a reduction in the time the tank was exposed to fire, in testing it was 1/3 less likely to be seen while maneuvering than the M60, and it could run a 10 km (6.2 mi) obstacle course in 30% less time.
An unanticipated problem 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 120mm gun proved excellent, but the XM-150 gun/launcher had serious problems. The similar but smaller XM81 gun/launcher mounted on the M551 Sheridan proved to be just as troublesome. There were also several problems with the ammunition. The caseless design made conventional tank rounds too vulnerable to water. Wet rounds expanded so they would not fit into the barrel anymore or left hard residues after being fired. The auto-loader was capable of handling the Shillelagh missile without problems, but the combustible cases of the tank rounds could be deformed by it. As is often a problem with caseless ammunition, the ammunition also 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 overcomplicated and nearly impossible to use effectively.
Another problem of the MBT-70 was the increasing weight. While at the beginning of the project, a weight of some 46.3 tonnes (45.6 long tons; 51.0 short tons) was projected, it increased to 54 tonnes (53 long tons; 60 short tons) during development, which forced the designers to redesign some elements, so that finally a weight of 50.3 tonnes (49.5 long tons; 55.4 short tons) was reached, still higher than required. This meant that the MBT-70 would require its own armoured recovery vehicles and bridge-launching systems.
In order to power the tank at the required speed, a turbine engine was developed for the original American model. However, turbine engines need very clean air, and the quantities of dust churned up by tank operations proved problematic. After initial efforts to solve the problem using air filters, the turbine engine was replaced with conventional piston engines.
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. Senator James W. Fulbright, mentioned that to drive a MBT-70, a master's degree in a technical institute would be required.
By 1969 the MBT-70 cost five times what was projected, at $1 million a unit ($6.53 million in present-day terms). Originally the planned costs of the MBT-70 project were as low as $80 million (or 292.8 million DM), but in 1969 the project had already cost $303 million (nearly 1.1 billion DM). West Germany's part alone of this was about $130 million (475.8 million DM), which in itself was more than the original planned total costs of the project. Germany backed out of the project, and started the development of the Keiler on its own. Later this program would lead to the Leopard 2. The Leopard 2, like the Keiler, uses a 120mm smoothbore gun.
In light of these problems, a complete review of the project was requested by US Deputy Secretary of Defense David Packard, and on January 20, 1970, the joint program was officially canceled by a Department of Defense news release. Work began on converting the existing MBT-70 design into a low-cost "austere" alternative that would use only American-made components, resulting in the nearly-identical XM803 prototype. Despite these compromises, the XM803 design began to match the MBT-70 in complexity as development progressed, and was ultimately marked for cancellation by Congress in December 1971. The XM803 program was officially deactivated on June 30, 1971 and its budget redistributed to the entirely new XM1 design project, which led to the production-model M1 Abrams tank. While the M1 uses a conventional, but welded steel turret, suspension, and gun, it retains the use of the advanced armor materials and gas turbine engine developed for the MBT-70 project.
Altogether 14 prototypes and test-beds have been built, two of them were made of mild steel. Some of them have survived in museums and can still be visited today.One prototype is located in the US Army Ordnance Museum in Aberdeen, Maryland.
Another prototype is located in the Armor Museum Restoration Yard at Fort Benning, Georgia; Plus an XM803.
A mild steel prototype in bad condition can be seen in the Military Museum of Southern New England in Danbury, Connecticut.
One prototype is located in the Deutsches Panzermuseum Munster
Another is located in the Wehrtechnische Studiensammlung Koblenz