The title of this is a little misleading - it hasn't really got anything much to do with submarines. It's more an espionage thriller that sees some Nazi spies pinch a prototype shortwave radio transmitter that enables them to report shipping movements to an Axis submarine which then picks them off. In desperation, the authorities fire their top experts in the field in the hope that they will be able to track down these traitors if any of their erstwhile technicians are approached to finesse the radio. The rest of the film serves as a bit of a wartime fillip - we are never in any doubt as to the ending; the drama is over scripted, really quite poorly lit and cheaply made - but the unremarkable, workmanlike, cast keep it moving well enough for just over an hour. "I don't bargain with rats"...!