First, actual documents are hard to find. The organization of bomb disposal units was complex and changed as the war progressed. Later in the war, the Americans had added time-delay fuses to their bombs along with a motion detonator which would go into operation if the bomb was moved/rolled. However, like hand grenades, American bombs had pins in them that had to be removed before the actual drop. No sense in crashing without the pins still in the bombs.
Examine the following, especially the last two blocks (scroll down):
http://www.bombfuzecollectorsnet.com/page22.htm
Ed