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The Falcon is part of U.S. effort — known as Conventional Prompt Global Strike, or CPGS — to develop the capability to strike anywhere in the world with a conventional weapon in less than an hour.

CPGS is a new class of weapons that officials hope will address recent threats, such as terrorist nuclear weapons, and help reduce U.S. reliance on nuclear weapons as a strategic option.

“The services are under tremendous budget constraints right now,” said hypersonic flight advocate Richard P. Hallion, the former chief historian of the Air Force.

But he urged the Pentagon to push ahead with other approaches to hypersonic flight, which he called “a critical defense technology.”