Misunderstandings about Murphy?

Many reviewers seem to take it that, as sole survivor of a torpedoed merchant ship, Murphy is a civilian seaman who embarks on a personal one-man war of revenge. Largely the fault of the film makers, but isn’t that a major misunderstanding?

On the right sleeve of his boiler suit Murphy wears the trade badge of a horizontal two-bladed propeller over the letter E. This indicates that he is an Air Mechanic (Engine) in the Fleet Air Arm of the Royal Navy. As a naval rating on active service, he gets back to his job of fighting the Germans as soon as he is fit. He enlists the only ally he can find in Louis, a citizen of now-liberated France. He brings back into service the only weapon he can find, the ship’s aeroplane that he used to maintain. And he carries on with the war.

You could say that since Murphy is no longer on the high seas but in Venezuelan waters, he should respect their neutrality. But hasn’t the U-boat captain breached that neutrality, without any reaction from the Venezuelan authorities? Desperate to conceal war crimes committed, instead of surrendering openly the captain hides his submarine up a creek.

You could say that once Murphy hears on the radio the news of Germany’s surrender, he should stop. The U-boat captain also hears the news, but that does not stop him firing first guns and then a torpedo at Murphy’s unarmed vessel. If the Germans are still making war, doesn’t that justify Murphy’s final response?