Decades ago, the destroyer USS Roper sank the Nazi submarine U-85 with all hands going to a watery grave. This was not an unusual occurrence. During World War II the Nazis lost 629 U-boats to a number of hostile acts, from being depth-charged by ships to hitting mines to being bombed while pierside at a port. But in 2003, U-85 briefly hit the news when its Enigma machine was "retrieved" from the shipwreck by some divers.
Eventually the Naval Historical Center managed to arrange the machine's donation to a North Carolina museum, but it highlighted a problem. The Navy also got a public-relations black eye over a recovered Brewster F3A. The Navy didn't like having to hand over the plane – even if it was a Corsair In Name Only.
As part of the 2004 defense authorization bill signed by then-President George W. Bush the "Sunken Military Craft Act" became the law of the land. The rules are intended to ensure that sunken wrecks of American military vessels (or aircraft) aren't tampered with.
The law does that by setting up very steep civil penalties — we're talking a $100,000 for each violation. What is a violation? Well, according to the text available at the website of the Naval History and Heritage Command, engaging or attempting to engage in, "any activity directed at a sunken military craft that disturbs, removes, or injures any sunken military craft."
Oh, and they consider each day a separate violation – those penalties will be adding up. Furthermore, the provisions also state that "vessel used to violate this title shall be liable in rem for a penalty under this section for such violation."
Or in other words, your boat is subject to confiscation.
And if you think you're gonna be safe by looting something like U-85… think again. Any foreign government can ask the Navy to protect their wrecks off our shores. So, looting a foreign warship wreck can get you in just as much hot water as if you'd looted one from the United States Navy.
All is not lost for would-be looters. According to the law, there is an eight-year statute of limitations. But given that you face huge civil penalties, it's better to ask permission. Or better yet, leave the wreck alone.