Coinciding with the Tet Offensive, the siege of the US Marine Corps base at Khe Sanh had all the hallmarks of a disaster for the American forces. Vulnerable and remote from other major US bases, the taking of Khe Sanh would be a major victory for the North Vietnamese and a massive blow for American morale. However, the use of air power and the determination of the Marine Corps defenders turned a potentially disastrous defeat into a military and propaganda victory. The North Vietnamese build-up in the area started in December 1967 and by 20 January about 20,000 North Vietnamese troops stood ready to attack the base. However, any hopes that the North Vietnamese may have had in replicating their famous victory over the French at Dien Bien Phu, which effectively marked the end of the Indo-China War in May 1954, were soon dashed. The major difference between the sieges at Dien Bien Phu and Khe Sanh was the availability of aerial firepower. In what became known as Operation Niagara, the US forces were able to muster the full strength of over 5,000 fixed-wing aircraft and helicopters against the enemy in the defence of Khe Sanh. A major factor in the ability to defend Khe Sanh on the ground was the resupply operations flown by C-123s and C-130s. Altogether these aircraft made 452 landings and 658 parachute drops to the encircled Marines bringing in 12,400 tons of ammunition and other supplies. Throughout the 77-day siege, US tactical aircraft together with B-52s maintained an unrelenting cascade of bombs, napalm and rockets on enemy positions while transport aircraft and helicopters kept the garrison supplied with ammunition, food and reinforcements. The B-52s alone flew 2,548 sorties dropping over 60,000 tons of bombs in defence of Khe Sanh, sometimes within 1,000 feet of the perimeter wire. It was the availability of air power at a sufficiently high level that made the difference between defeat and victory for the US forces at Khe Sanh.