Insiders liken it to a "panic button.” For more than 80 years, the primary job of the National Defense Stockpile (NDS) has been to keep the U.S. military supplied with essential raw materials and protect against supply shocks.

So when China surprised the markets by restricting exports of two niche industrial metals last year, top-level officials in the Pentagon-controlled agency — and the White House — faced an uncomfortable reality: Its panic button no longer worked.

The realization triggered a different kind of alarm in Washington.