amazing swiftness, splitting the Saigon forces and wiping out one position after another. The tactic of mobile defence by tanks and infantry has also proved ineffective. At the Dong Ha-Quang Tri defence complex, the US command had deployed a big defensive force inside heavily-guarded strongholds and also organised .strong mobile units of tanks and infantry. Saigon troops were stationed at one place in daytime and at another at night. Such a mobile defence outfit was usually made up of electrically detonated mine fields on the outer perimeter, a row of tanks and finally infantry troops.