The M-10 was America's first tank destroyer built on a Sherman hull with a 76mm 50 caliber cannon. The cannon was so heavy a counter-weight had to be mounted on the rear of the turret. It had light angular armor and counted on speed and agility for survival. Extra armor could be bolted to the turret and hull. The turret had an open-top exposing the crew to enemy fire and the elements. The M-36 with its 90mm cannon eventually replaced the M-10.