These light amphibious recce tanks were used by the North Vietnamese Army in the later stages of the war
“The first successful action of NVA armor in Vietnam was against the Lang Vei Special Forces camp on 6/7 February 1968 (they had already been used in the preceding Battle of Ban Houei Sane, which was just across the border in Laos however). Thirteen PT-76s, of the NVA 202nd Armored Regiment spearheaded an assault against approximately 24 Green Berets, 500 Vietnamese irregulars and 350 Laotian Royal soldiers. The defenders fought back with their 106 mm M40 recoilless rifle (one at the entrance took out three PT-76s until it was knocked out), and ineffectively with M72 LAWs (one-shot disposable 66 mm Light Anti-Tank Weapon). They requested support from nearby Khe Sanh, which was unable to help, as it too was under siege. The Lang Vei camp was overrun, with the PT-76s using their turret-mounted spotlight-equipped heavy machine guns to shoot down any irregulars who panicked and ran out of the underground bunkers. A few survivors broke out and were airlifted to safety.
“The first tank-to-tank engagement occurred in mid-1968 when a US reconnaissance airplane observed a PT-76 being washed by its crew in the Bến Hải River in the DMZ(17th Parallel). The Forward Air Control pilot radioed the tank’s position to a nearby M48 Patton tank unit of the US 3rd Marine Tank Battalion. With the FAC adjusting fire, the Patton fired three 90 mm rounds; obtaining a hit with the third round. The tank crew abandoned their vehicle. Shortly afterwards, some returning F-4 Phantom jet fighter bombers, with ordnance to expend, observed the PT-76 and bombed the remainder of the vehicle.