WWII silver-wound magnets from Fort Knox

Copper shortage during WWII forced Manhattan Project to borrow ~50 tons of silver from the U.S. Mint in Philadelphia for the Calutron magnetic separators at Oak Ridge; returned after the war undamaged.

Although during World War Two when they were separating uranium in the magnetic separators at Oak Ridge — it was basically a great big mass spec, they were separating uranium-235 from 238 — they had a shortage of copper. All the copper was being used for shell casings for the guns. It turns out they borrowed something like fifty tons of silver from the U.S. Mint in Philadelphia, and they wound their magnets out of silver for Oak Ridge to make the nuclear weapon. After the war they had to return the fifty tons to the U.S. Mint because it didn't deteriorate in service. Silver is the only thing that would be better to wind the electrical windings of a great big motor — unless you have a superconductor that works. That's another story; I could spend an hour on that about high-temperature superconductors and whether they're going to make big magnets.