Editing M1 Abrams (section)

===Prototypes===
[[File:XM1 Chrysler prototype.png|thumb|Chrysler XM1 prototype]]
[[File:General Motors XM1 Tank Prototype Under Evaluation at Aberdeen Proving Grounds, 1976.jpg|thumb|General Motors XM1 prototype]]

Prototypes were delivered in 1976 by Chrysler and GM armed with the M68E1 105&nbsp;mm gun. They entered head-to-head testing at [[Aberdeen Proving Ground]].{{sfn|Hunnicutt|2015|p=189}}{{sfn|Hunnicutt|2015|p=189}} The testing showed that the GM design was generally superior to Chrysler's, offering better armor protection, and better fire control and turret stabilization systems.<ref name=bail/>

During testing, the power packs of both designs proved to have issues. The Chrysler gas turbine engine had extensive heat recovery systems in an attempt to improve its [[fuel efficiency]] to something similar to a traditional [[internal combustion engine]]. This goal was not achieved: the engine consumed much more fuel than expected, burning {{convert|890|L/100km|usgal/mi|sp=us}}. The GM design used a new variable-compression diesel design.<ref name=bail/>

By spring 1976, the decision to choose the GM design was largely complete. In addition to offering better overall performance, there were concerns about Chrysler's engine both from a reliability and fuel consumption standpoint. The GM program was also slightly cheaper overall at $208 million compared to $221 million for Chrysler. In July 1976, the Army prepared to inform Congress of the decision to move ahead with the GM design. All that was required was the final sign-off by the [[United States Secretary of Defense|U.S Secretary of Defense]], [[Donald Rumsfeld]].<ref name=bail/>