 Twenty-five Lancasters dropped the first Tallboys on the mountain, penetrating straight through the rock, and one of them exploded in the tunnel below.As a result, the entire rail line remained unusable until the end of the war.The Bielefeld viaduct was only closed for brief periods by 54 raids dropping 3,500 tons; but in its first use on 14 March 1945 the "Grand Slam" destroyed whole sections of the viaduct.