How was the bridge blown up?
I never saw or heard mentioned the existance of demolition charges. The soldiers in the river were only shown with hand grenades.
shareWe must assume that demolition charges were used, since demolition of the bridge was the platoon's primary task. The sergeant who carried a hand grenade (actor Lloyd Bridges, if I remember correctly) probably intended to use it against the German guards patrolling the bridge.
The massive explosion shown on screen could not have been produced by hand grenades, even if detonated simultaneously.