The M60 is an American second generation main battle tank (MBT). It was officially standardized as the Tank, Combat, Full Tracked: 105-mm Gun, M60 in March 1959. The program to develop the M60A1 was approved in early 1960 in conjunction with abandoning further development of the advanced composite armor and the closure of the T95 Medium Tank project. The first proof of concept attempt to mate a modified M60 hull with the T95E7 turret took place in March 1960. The turret, even without the siliceous cored armor, provided improved ballistic protection. Additional space for the turret crew was also made available by using the M140 mount thus moving the cannon 5 inches forward. The first two prototypes were ready in May 1961 and the third in June 1961, when the vehicle also received its official prototype designation as the M60E1. These vehicles were built by Chrysler Defense. Prototype 1 was sent for evaluation at the Eglin Air Force Base climatic hangar, while Prototype 2 was tested at the Yuma Test Station, and Prototype 3 underwent field trials at Fort Knox. On 22 October 1961, the M60E1 was officially accepted in service under the designation of Tank, Combat, Full Tracked: 105-mm Gun, M60A1. Production began on 13 October 1962 when the Army placed an initial order for 720 of the tanks.