Staged sequences of "saboteurs" planting underwater explosive charges (Malta ?).
I. Night sequence. 'Saboteur' on a paddle board passes between two moored destroyers.
II. Underwater sequence as two frogmen leave a cliff-side and swim off - they make towards the camera situated under ship's keel. One diver goes to the surface to reconnoitre. Saboteur places plastic explosive in ship's main underwater vent - the camera closes to give a CU of the explosive charge.
III. MS as RN diver searches around ship's screw with an underwater light. He moves along the bottom of the ship, sweeping the hull with his hands - another diver works along the bilge keel. Diver discovers a clamp mine attached to the bilge keel.