The ARVN defenders did have one card to play throughout the battle: the immense power of U.S. air support. The use of B-52 Stratofortress bombers (capable of carrying 108 MK82s (500 pound) bombs on one run) in a close support tactical role, as well as AC-119 Stinger and AC-130E Spectre gunships, fixed wing cargo aircraft of varying sizes, AH-1 Cobra attack helicopters and Republic of Vietnam Air Force (RVNAF) A-37s. These methods worked to blunt the PAVN offensive. At this stage in the war, the PAVN often attacked with PT-76 amphibious and T-54 medium tanks spearheading the advance, usually preceded by a massive artillery barrage. These tactics reflected Soviet doctrine, as the PAVN had been supplied with Soviet and Chinese Communist equipment, including jets, artillery, and surface-to-air missiles since the beginning of the war. The battle eventually stagnated and became a periodic trade of artillery barrages. This was most probably a result of casualties sustained in the frustrated attacks on heavily entrenched enemy positions in control of a withering array of supporting firepower.