During WW2, U-507 became the first U-boat to enter the Gulf of Mexico in 1942. One of her victims was the Alcoa Puritan which was sunk by gunfire and one torpedo.
The Alcoa Puritan was discovered in 6,400 feet of water. During a ROV expedition to the shipwreck, a 10.5cm shell casing was recovered from near the Alcoa Puritan shipwreck.
This is certainly one of the 75 shells fired by the U-507.
The shell casing was standing upright on the sea floor, note the line around the casing that was in the mud.