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 have better mobility 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 obstacle course in 30% less time. A year behind schedule, the U.S. and Germany debuted their MBT-70s publicly in October 1967. An American prototype was displayed outside the
Association of the United States Army in Washington. The German demonstration in Augsburg ended prematurely: smoke poured out of the tank after the turret's hydraulics malfunctioned. Observers were nonetheless impressed and German officials said the tank was on track to replace all M48 Pattons of the Bundeswehr by 1972.
Problems 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 XM150 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 was projected, it increased to during development, which forced the designers to redesign some elements, so that finally a weight of was reached, still higher than required. This meant that the MBT-70 would require its own armored recovery vehicles and bridge-launching systems. Germany became concerned with the excessive weight of the tank. One solution proposed removing radiation hardening from the turret, but this called into question the wisdom of the driver-in-turret configuration, which was intended to protect the crew in the event of a
nuclear blast. 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 quipped that to drive an MBT-70, a
master's degree from a technical institute would be required. ==Cancellation==