port and starboard rear of the vehicle, and a combination circular & flat frontal gun shield(s) were added around the .50 caliber machine gun located at the commander's hatch. This combination produced a M-113 Armored Cavalry Assault Vehicle, or, in Vietnam more simply referred to as an ACAV by GIs, a name coined by 11th Armored Cavalrymen. The regiment's modifications emphasized the use of ACAVs instead of the Patton medium tank and completely replaced the M-114 found in reconnaissance platoons, which may have existed in European and CONUS areas of operation. The M114 had been deployed to Vietnam in 1962, but withdrawn in 1964 due to its unsatisfactory, and often disastrous performance. Throughout the war, the tank companies, with their M48 Patton tanks, remained the same in each squadron. In 1968, Colonel George S. Patton IV (son of World War II General Patton), commander of the 11th ACR in South Vietnam recommended to General Creighton Abrams that one squadron from a division and the other from theater command be issued the army's new aluminum tanks (Sheridans) for combat testing. General Abrams concurred, and in January 1969, M551 Sheridans were issued to the 3rd Squadron 4th Armored Cavalry and the 1st Squadron 11th Armored Cavalry. Due to differences between the organization of regimental cavalry squadrons and divisional cavalry squadrons, in 1st Sqdn 11th ACR, the Sheridans were issued to the ACAV troops, replacing three M113 ACAVs in each platoon (the squadron's one tank company remained intact); in 3rd Squadron, 4th Cavalry, the Sheridans replaced M48A3 tanks throughout. Although the 3/4 Cavalry met near disaster with their Sheridans within a month of receiving them (one destroyed by a mine), the 1/11 Cavalry had just the reverse in luck, killing nearly 80 enemy soldiers during an engagement on 23 February 1969. All things considered, the army was satisfied with the Sheridan tank, and by the end of 1970 alone, well over 200 M551s would be in South Vietnam. While nearly all US armored cavalry squadrons were equipped with the M551 by 1970, the 11th ACR tank companies, as well as the three US Army armor battalions (1/69th, 2/34th, and 1/77th Armor) in country, all retained their 90mm gun M48A3 Patton tanks. Only the M48s, as well as the Australian Centurions, and ARVN M41 Walker Bulldog light tanks could effectively and safely conduct "thunder runs"; the firing of all tank weapons while driving down