The U.S. military has been talking about “stealth motorcycles” for years. As of this month, two tech outfits have what seem to be viable prototypes that will both be funded for another revision.

Trotted out at the Special Operations Forces Industry Conference in Tampa, Florida, the Logos Technologies “Silent Hawk” and LSA Autonomy “Nightmare” are both basically multifuel-electric hybrid two-wheel-drive dirt bikes capable of running as quietly as 55 decibels—about the volume level of an indoor conversation.

DefenseOne tells us these bikes are the answer to a challenge the Defense Advanced Research Projects Agency put to the defense industry about a year ago.

Top speed on both is said to be around 80 MPH, but the bikes are still range-limited in quiet-running electric mode. The SilentHawk is listed at “two hours” electric runtime and the Nightmare can reportedly make it 60 miles.

“With a skilled rider you can get basically anywhere on the planet,” SilentHawk lead engineer Alex Dzwill told The Washington Post. But since you’re not getting all that deep in two hours or 60 miles, both bikes have ancillary liquid-fuel powered engines to feed the motor once the liquid cooled lithium-ion batteries are depleted.

At least those charging-engines are versatile; apparently capable of burning the military’s ubiquitous JP-8, Jet A-1, gasoline, propane, diesel or kerosene if necessary. Even lipids like olive oil would work “theoretically,” according to what Dzwill told reporters at the conference.

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