I've got a pic in one of my many B-24 books, showing a cluster (of 3 ?) tubes beneath the tail of a B-24. Can't get to it at the moment, as my arms are too stiff to get the book off the shelf !
From memory, these were mounted just aft of the rear belly hatch, and fired aft, from inside the aircraft, the intention being to at least disrupt attacks from the rear, but the idea was soon abandoned.