U-Boats threaten sea routes (00/02/1943): LS of ships in convoy. Cut to action stations on submerged U-Boat (00/02/1943). MS of U-Boat officers on the conning tower at night and LS of boat exploding in the distance (00/02/1943). View from conning tower as camera U-Boat moves on surface during storm (00/02/1943). Sequence as crew battens down the hatches from inside the submarine, submarine diving as seen through a periscope, captain looking through the periscope. Periscope view of the sea. Surface shot of the periscope cleaving the water (00/02/1943). MS of freighter being hit by a torpedo, sinking, exploding in a tremendous blast. Shot of depth charge going off, as seen from a corvette (00/02/1943). AERIAL SHOT of dozens of ships in a convoy (00/02/1943).