The M60’s replacement, the M1A1 and M1A2 Abrams, is today probably the top MBT in the world. It began as a joint project by West Germany and the United States for a new MBT that could engage and defeat the vast number of tanks the Soviet Union might field in an invasion of Central Europe. Designated the MBT-70, this new tank was to feature the Shillelagh gun/missile launcher and a 1,500-hp engine, neither of which was working out as planned.
Collapse of the MBT-70 project and cancellation of the follow-on XM803 program led to a brand-new program, which literally began from the ground up in 1972. The MBT-7O/XM8O3 programme was terminated at the end of 1971 and in the following year the US Army embarked on the development of yet another tank, originally designated XM815. The new tank, which became the XM-1. was to be simpler and less costly than the MBT-70/XM803 and it was to be developed relatively quickly in view of the US Army’s increasingly urgent need for a new battle tank. Moreover, the highest priority was no longer to be accorded in its design to fire-power, as it was in the case of MBT-70, but to crew survivability.
All this led to a tank with a conventional configuration and a four-man crew but with much better protection than earlier US tanks. The latter was particularly effective against shaped charge weapons, thanks to the adoption of the Chobham armour which had been developed in Britain. To help increase its survivability, it was also significantly lower and it had no commander’s machine gun cupola to ruin its silhouette.
To reduce development costs, its components were chosen to a large extent from those already in existence and in particular from those developed as part of the MBT-70 programme. The latter included two alternative engines, both of which developed 1500hp. This made the XM-1 very agile even though it was somewhat heavier, at 52.6 tons, than the MBT-70.
The XM-1 was no longer required to fire guided missiles and in view of this and the problems encountered with the 152mm gun-launcher of the MBT-70 the only course that was open was to go back to the 105mm gun which had been used already for 13 years in the M60 tanks. This retrograde step was made inevitable by the rash decisions taken by the US Army in 1957 to concentrate on guided missile launchers, which caused it to abandon the development of new tank guns. To be fair, the adoption of the 13-year old 105mm gun was alleviated by the contemporary development of APFSDS ammunition which made it more effective than it had been before. Some consideration was also given to retrofitting at a later stage a 110mm gun which was being developed in Britain. However, the latter proved no better than the 105mm gun with its new APFSDS ammunition during trilateral gun trials carried out in Britain in 1975. This was due to the fact that the 110mm gun was still only provided with APDS ammunition, to which its British developers remained wedded, in spite of the evidence that APFSDS ammunition was becoming superior to it, because of the success they had with it until then.
The actual development of the XM-1 was carried out on a competitive basis, contracts for it being awarded in 1973 to Chrysler and to General Motors. Both companies completed their prototypes in 1975 and after trials the Chrysler XM-1 was chosen in 1976 for further development on the grounds that it was being offered at a lower cost. The principal engineering difference between the two was that the General Motors prototype was powered by a variable compression ratio diesel. which was not entirely successful, while the Chrysler prototype was powered by a gas turbine, which was expensive to produce and which, in spite of repeated claims to the contrary, proved to have a high fuel consumption. A conventional diesel would have been a better choice for either of the two designs and one of 1500hp had been developed in Germany for the MBT-70 but it was not considered for the XM-1.
Whichever of the two US prototypes won, it was intended that it should be evaluated in competition with the German Leopard 2 with the view of achieving standardisation between the US and German tank fleets, ostensibly even to the extent of adopting the same tank for both. In the event all that happened was that the US Army decided in 1978 to adopt the 120mm smooth-bore gun produced in Germany for the Leopard 2. The decision was taken after trials carried out in 1977 when the German 120mm smooth-bore gun was compared with the US 105mm tank gun. which by then was 18 years old, and a new 120mm rifled gun hastily developed in Britain to suit US requirements.
Having won the competition, Chrysler produced the first of a pre-production batch of eleven XM-1 tanks in 1978 and in 1980 began to build M1 tanks, still armed with 105mm guns. It was originally intended to produce a total of 3312 M1 tanks but by 1985 their number was increased to 7467. Of this total 4199 were to be M1A1 tanks armed with 120mm guns, the first production model of which was completed in 1985. By then the responsibility for the M1 had passed to the Land Systems Division of General Dynamics, who had taken over its development and production from Chrysler in 1982.
The new tank was named for General Creighton Abrams, armor tank battalion commander in World War II, Allied commander in Vietnam, and army chief of staff.
The M1 was a revolutionary design as well as a sharp departure from previous U. S. tanks, with their rounded surfaces and relatively high profiles. The M1 was more angular, with flat-plate composite Chobham-type armor, with armor boxes that can be opened and the armor changed according to the threat. At 8 feet tall, it is also considerably lower than the M60 (10 feet, 9 inches). From the start, the army’s intention was to arm the M1 with the 105mm gun. As a result of a program aimed at securing a common main armament for U. S., British, and West German tanks, the decision was taken, after initial M1 production had begun, to arm the M1 with a German-designed Rheinmetall 120mm smoothbore gun. But that gun was still under development when the tank was ready, and so the army decided to continue with the 105mm M68 gun utilized in the M60. The 120mm M256 gun, essentially the German designed gun with a U. S. breech, was available in 1984, and the first M1A1 with this new armament came off the production line in August 1985. The M1A1HA introduced a new steel-encased depleted uranium armor, which is virtually impenetrable, but it also dramatically increased the tank’s weight to nearly 146,000 pounds.