How were some of the NVA tanks stopped during Vietnam?

Answer 1

Unfortunately for the NVA, the allies had aircraft everywhere all the time. Which is why they were smart enough not to field them in the open very much. The vast majority of NVA armor was knocked out by jets (or blasted into scrap metal by B52s). US Patton tanks did knock out some PT76 light tanks at Ben Het in '68, those were hit with the Patton's 90mm main guns. The Patton could fire 2 types of anti-tank rounds: HEAT & SHOT, but for a PT76 a standard 90mm HE round could do.

In 1971 (Laos invasion/Operation Lam Son 719) ARVN M41 light tanks engaged NVA armor, those guns were 76mm. In 1972 the US employed TOW anti-tank missiles fired from choppers. They knocked out over two dozen NVA tanks, both T54 & PT76. First time that system was used.

Green Berets at Lang Vei knocked out some NVA PT76 tanks with the standard M72 LAW (the US version of the communists RPG) in '68. The US LAW rocket is 66mm. Unlike the RPG, the M72 cannot be reloaded, it's "shoot and toss" (after you wreck it a bit so the enemy can't use it to fire 60mm mortars with).

None of those systems "destroyed" a tank, they just punched holes in them. Air strikes could destroy a tank. 750lb and 1000lb bombs can turn a tank into scrap metal. Choppers and jets also fired 2.75" rockets at tanks, but although the air force says they were effective, some GIs on the ground think otherwise.