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 . The suspension could be raised or lowered on command by the driver , down to put the bottom of the tank just over from the ground , or up to 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 missile s , then one of the most dangerous weapons deployed against tanks . The design included bulkhead s , 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 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 . German versions originally used a similar Daimler - Benz model , but later moved to an MTU design of . The MTU unit could be easily swapped out of the tank , along with the drive train , in 15 minutes . Both versions could reach 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 restarted 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 .