What ship, known for its unusual and somewhat controversial design, was intended to be a fast, lightly armored commerce raider during World War II, but spent most of its career as a target ship?

1. It was designed with a single, large, forward-mounted gun.
2. It possessed a very high length-to-beam ratio, giving it a very slender profile.
3. Its design was a product of the German Kriegsmarine.
4. It was ultimately sunk by a torpedo during a postwar weapons test.