There's one thing that cannot happen on board a submarine by accident... is both ends of a torpedo tube open to the sea at the same time!
You cross-connect the hydraulic manifold to the outside door mechanism so that the indicator reads shut when the door is actually open. The same sort of electrical cross on these two panels, and the open position reads green when it should flash red. Then you plug up the inlet to the test cock with chewing gum, sealing wax, anything... just so that it shows a dribble. And then you open the tube, and Good Night.