Mystery Submarine

''U-153'' is damaged during air attack in the Atlantic, and its crew abandon to escape Chlorine gas leakage due to broken battery cells. Her commanding officer is overcome by fumes before he can jettison the ship’s papers. Aware of the intelligence windfall that this represents, the submarine is taken by a British prize crew to be examined and inspected (in much the same manner that befell the real German U-boat later renamed HMS Graph ).