American navy practice using remote control to detonate mines to attack submarines.
Full title reads: "Hampton Roads, Virginia".
United States of America (USA).
VS of a ship - presumably American Navy - sailing in the sea off Virginia. They appear to be laying mines.
Int. operations room on ship, they look at charts and use viewing devices.
LS submarine periscope just above water.
VS officers look through telescopes and drops hand to signal firing mine.
LS explosion by submarine. More shots of the process of discharging mines in exercise to attack submarine.
N.B. Item found in Unidentified Gazettes reel. Matches missing item from 36/56 (LNER).