It was on a submarine, and they were sailing on a secret mission to attack a German port or something.
The chief mechanic was always muttering about how Hitler really should be in charge, and how the King was a flake, and how the Empire was a sorry place.
The commando officer overheard this and went to the Captain of the sub asking why a traitor was on board.
The Capt. laughed and said something about not taking that old bloke seriously. He was just talking to let steam off.
Later in the movie of course the mechanic turned up to do some heroic self-sacrifice in keeping the sub safe.
It was very cute.
I think of Bowser in that context: very likely just crankishly blowing off steam.
No one could actually be concious and as twisted as he comes across.
Ed