The Navy will now take that data to help in future ground testing, as well as for modeling and simulating hypersonic flight characteristics. Evans said the design could potentially fit in with a wide array of unspecified “Conventional Prompt Strike concepts.” These would likely be the kind of time-sensitive situations we have previously discussed, including critical enemy facilities, specific weapon systems, or even a specific individual or group of individuals.

Pentagon spokesperson U.S. Navy Commander Patrick Evans confirmed the test, formally called Intermediate Range Conventional Prompt Strike Flight Experiment-1 (CPS FE-1), to USNI. “The test collected data on hypersonic boost-glide technologies and test-range performance for long-range atmospheric flight,” he explained, suggesting this new vehicle could be another unpowered glider.

“I’m very proud to report that at 0300 on Monday night SSP flew from Hawaii [Pacific Missile Range Facility] … the first conventional prompt strike missile for the United States Navy in the form factor that would eventually, could eventually be utilized if leadership chooses to do so in an Ohio-class tube,” U.S. Navy Vice Admiral Terry Benedict, director of SSP, said on Nov. 2, 2017, according to USNI News . “It’s a monumental achievement.”

But most notably, earlier in November 2017, the U.S. Navy’s Strategic Systems Program (SSP) revealed it had test fired a hypersonic vehicle from the Pacific Missile Range Facility in Hawaii. Though the service offered few details about the experiment or the craft itself, it is almost certainly a prototype conventional weapon rather than a purely research design.

Arming an the Ohio-class submarine, which can stay largely hidden underwater for weeks at a time, with this type of weapon would only make it more flexible and harder for an opponent to detect and react to the strike. One obvious scenario for one of these hypersonic weapon-armed subs would be as part of the opening salvo of any attempt to neutralize North Korea’s nuclear and ballistic missile capabilities in the event of an actual conflict on the Korean Peninsula.

The fast-flying weapons could take out wily ground-mobile ballistic missiles as they are being fueled for launch or air defense sites ahead of sorties by B-2 bombers carrying the GBU-57/B Massive Ordnance Penetrators that would be necessary to actually have any chance of hitting at the primary targets, which the North Koreans have buried deep underground, from the air. One of the Ohio-class guided missile boats, the USS Michigan, made a visit to South Korea's port city of Busan in an apparent show of force in October 2017.

It's unclear whether the Navy is planning to make the hypersonic weapon an option for the four Ohio-class boats configured as conventional missile submarines or for the class as a whole, including the nuclear-capable members. At present, of the legs of the U.S. military's nuclear triad, only the U.S. Air Force's strategic bombers have this dual capability mission.

Critics have long argued that a hypersonic boost glide vehicle, which requires what is essentially a ballistic missile to get up to speed, could be a destabilizing weapon. Their main concern is that a peer state competitor would detect the launch of a submarine-launched ballistic missile and would be unable to distinguish it from a nuclear first strike, and would be likely respond as if it were.

Smaller countries with limited deterrent capabilities might feel especially threatened and be likely to adopt a worryingly aggressive alert posture to launch a retaliatory strike just upon detecting a potentially hostile launch, according to a report the RAND Corporation released on the topic in September 2017. The think tank argued broadly for international nonproliferation agreements between countries developing such weapons, akin to nuclear weapons.