Old Tank, New Gun During the 1960s, the Israeli Defense Forces upgraded their M4A1 Sherman tanks by equipping them with the powerful French 105mm CN-105-F1 tank gun and they were redesignated as M51s. A muzzle brake was installed to minimize the greater recoil effect and a large counterweight was fitted to the rear of the turret to offset the long barrel. The 460hp diesel engine and the combination of the Horizontal Volute Spring Suspension (HVSS) and wider T80 tracks gave the M51 improved mobility. During the Six-Day War in 1967, the M51s were used against newer T-54/55 tanks as well as JS-3 tanks from Egyptian, Iraqi, and Syrian armies and proved their superiority.