Take a look in the section called Weapons in WWII, and then the aviation linkfest at the top. That should keep you busy for at least 10 years !!!
In the late 30's I don't think they had engines strong enough to lift a heavy seaplane/flying boat and four torpedoes, plus fuel and still be built strong enough for sea duty. Anouther problem for sea aircraft is salt water spray eats all things metal. Keeping the aircraft out to sea with no fresh water spray downs would make them very short lived for the investment.
There are a string of islands in mid Atlantic that belong to Portugal that the Germans could have taken for an aircraft base but I guess they did not think of it. (Portuguese are not too bright so taking them would be a push over.)
Can't get midget submarines to central Texas.
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