Tank origin

The U.S. military’s continued search for an acceptable design for an air-mobile armored vehicle led to the development of the M551 Sheridan, which began in 1959. Key to its design was to be the 152mm gun, which would fire cannon rounds as well as Shillelagh guided missiles. The tank experienced recoil upon firing, however; additionally, the all-aluminum hull provided little protection against ground mines. Although its design made it unpopular during the Vietnam conflict, the M551 Sheridan nevertheless remained in service into the 1990s.