The first prototypes were presented in 1976, and in both, all the superfluous and technologically very complex components were eliminated. Priority was given to reliability, service availability and firepower. The picture shows the prototype from General Motors that was named as “XM-1“, (as the one of Chrysler), since this was the name given to the new battle tank’s project. This prototype was the more conventional of the two from an automotive point of view and was armed with the same 105mm rifled gun as the Chrysler prototype.This is another picture of GM’s XM-1, equipped with a 1,500 hp Teledyne Continental AVCR-1360-2 variable compression diesel engine, air cooled and supercharged. It was coupled to a Detroit Diesel Allison X-1100-1A automatic cross-drive transmission with 4 forward gears and 2 reverse. This prototype incorporated a hydrostatic steering and integral services brakes. The suspension installed was a National Water Lift hydropneumatic with torsion bars.This is the XM-1 prototype presented by Chrysler, in which the main difference was in having a drive train composed of seven smaller roadwheels instead of six. The turret had a more rounded and smooth appearance and the front glacis was much flatter than the GM model. In addition, the rear deck was tilted upwards from the last two roadwheels, providing more room for the engine.The Chrysler prototype in the picture was powered by a 1,500 hp AVCO Lycoming AGT-1500 gas turbine. It was coupled to Detroit Allison’s X1100-3B hydrokinetic transmission that controlled the automatic gearbox with 4 forward gears and 2 reverse gears. This vehicle operated a wet disc braking system and an infinitely variable hidrostatic steering. The set weighed about 1,950 kg, of which 1,132 kg belonged to the gas turbine.GM’s prototype had the crew, the fuel area and the ammunition area located in different compartments. In this way, if any of these areas received an impact, the others would be much less damaged. On the left side of the turret, (according to the image), you can see the laser rangefinder that was completed with a day/night optics and with a two axis independent stabilized line-of-sight fire control system.
The GM’s XM-1 prototype complied with all the Army’s requirements and had excellent maneuverability, was easy to operate and had good accessibility for the crew. The main characteristics were: Weight of 58 tons, the hull measured 7.60 meters length, 3.65 meters width and 2.35 meters height. It reached 79 km/h and had an operation-to-maintenance ratio of 1 to 1. That is, it needed 1 maintenance hour per 1 operation hour, a similar ratio to the M-60 tank.Mobility in the Chrysler’s XM-1 tank was another of its strengths and according to some sources the tank was capable of reaching 100 km/h!!. It could travel 500 km at an average of 50 km/h and was capable of accelerating from 0 to 33 km/h in only 7 seconds. The gas turbine operated with diesel fuel and it was estimated that it could operate from 20,000 to 30,000 km without an overhaul.It was the first time that a turbine gas was used in a battle tank and there were doubts about its performance. Finally it was clear that use on the Chrysler’s XM-1 was entirely feasible and for example, the turbine delivered its highest torque at low revolutions. This was suitable for heavy acceleration or to provide the tank with an excellent climbing ability. Some drawbacks were the difficulty of starting at very low temperatures and excessive fuel consumption.Chrysler’s XM-1 mounted the same 105mm rifled gun as the GM prototype, although both models were designed to carry the 120mm gun. Finally, Chrysler’ prototype won the XM-1 contest and its main characteristics were: Weight of 54 tons, 9.72 meters of total length, 3.58 meters width and 2.37 meters of height to the roof of the turret.After its victory, Chrysler received another 196 million dollars to build 11 pre-serie XM-1 prototypes, (like this one on the picture). With these vehicles, the last tests should be started before manufacturing. It was at this time that German cooperation was again attempted in the project in order to be able to manufacture common components for the future M-1 and Leopard 2 tanks. Unfortunately again, collaboration was a fiasco and both countries ended up manufacturing their own tanks separately.The pre-serie’s XM-1 carried a modified turret to carry indistinctly the 105mm or 120mm gun, as the prototypes. Externally the frontal part of the turret looked like the one of the GM’s prototype due to the new armour. In this stage the smoke grenade dischargers of British design were installed on both sides of the turret. In addition a manual hydraulic system to adjust the tracks in case of slack out or by mine damage was also installed, allowing the tank to continue rolling and leave the combat zone.During trials stage carried out at Fort Bliss since summer of 1978, numerous bugs and problems with the pre-serie XM-1s were leaked to the press. There were problems due to the ingestion of dust in the turbine, problems with the gearbox and malfunction of the fuel supply circuit. To the previous ones we had to add serious failures with the aluminum tracks, that came out and broke and were worn out in excess, and a huge list of problems considered as “minor ones”.At the beginning of the tests, the pre-serie XM-1 was required to run an average of 438 km without failures, as well as 1 of every 2 tanks could travel 6,500 km without changing the engine. Nevertheless, the average obtained was 233.5 km trips between failures and that only 1 in every 4 tanks did not have to change the engine earlier than required. After arduous works and numerous modifications, in February 1980 the average between failures had reached 493 km and 1 of each 2 tanks managed to cross the 6,500 km with the same engine. These figures showed that reliability had been greatly improved.Despite its difficult development, the main problems of the XM-1 were solved before the M-1 General Abrams left the assembly line. Finally, the US Army has had since 1980 one of the most reliable and powerful battle tanks in the World. Despite the inconveniences of a new model, any American “tanker” asked, always declared that: “Abrams is the best vehicle with which they have worked”. The maintenance personnel also benefits from accessibility for repairs and easy maintenance of this model.
