Answer: Scientific Instruments

At the end of the first World War, the Germans scuttled their own navy, sending the remains of the Imperial German fleet (a.k.a the High Seas Fleet) into the salty waters off the coast of the Orkney Islands. Although salvage crews eventually recovered many of the ships, a number of them were left in the shallow waters and largely forgotten.

Forgotten, that is, until decades later when a large supply of steel uncontaminated by nuclear explosions and testing was required. It was so expensive to create new steel that was uncontaminated by traces of radioactive fallout that steel from the old German navy was lifted from the sea floor and used in a wide variety of applications where freedom from radioactive contamination was critical, such as in the construction of enclosures for scientific instruments that would accompany the Apollo missions and ride along in space probes like those built for the Pioneer and Voyager programs.

The graveyard of the German fleet remains the largest source of pre-nuclear age steel.