The launch happened hours after South Korean and U.S. troops kicked off their large annual combined drills, which the North views as an invasion rehearsal.
South Korean and U.S. militaries halted all live-fire exercises across South Korea after South Korean jets mistakenly released bombs on a civilian area.
The U.S. is in a race to field the capability and develop systems to defend against hypersonic missiles, which China and Russia are developing and testing.
The Army's research facility includes a permafrost tunnel — about a third of a mile long — that has Ice Age-era animal bones jutting out from the walls.