The U.S. military is already investing tens of billions of dollars to make its jet fighters less visible to radars and infrared sensors. Now the Pentagon wants the defense industry to come up with a system that can cloak fighters from another telltale type of radiation: ultraviolet energy from the sun.

The Navy's latest solicitation to research proposals asks for a "UV obscurant device" that can be "dispersed from an aircraft." The system should be compatible with the Navy's existing counter-measures dispensers, which are currently tailored for releasing infrared flares and radar-foiling chaff to help warplanes dodge enemy missiles.

A UV cloak would complement the Navy's other stealth initiatives. The F-35 Joint Strike Fighter, the product of history's most expensive weapons program, is designed to scatter and absorb radar waves while also sinking its engine heat into its fuel load in order to make the plane less visible to infrared sensors. The Navy plans to purchase hundreds of carrier-compatible F-35s at more than $100 million a pop.

But the F-35's design apparently does not protect against ultraviolet sensors – that we know of. The Navy's older Hornet fighters are probably equally vulnerable. The UV cloak seems to be a response to a particular type of "dual-band" missile seeker that zeroes in on infrared radiation at first, then switches to a UV sensor in the final moments before striking the target. The UV sensor works by looking for non-reflective shadows against the bright UV glare of the sky – like silhouettes against a lightboard.

An obscurant could blot out a plane's UV silhouette in a shapelesss mass of ultraviolet shadow. "One concept might include a device that very rapidly generates an extended, dense cloud of material that absorbs in the UV region," the Navy solicitation reads. The solicitation also lists "quantum dots" (tiny radiation-emitting crystals) and man-made "metamaterials" as obscurant options.

The obscurant would probably work on helicopters, too.

The solicitation does not specify a delivery timeframe or a cost cap. But if other forms of sensor-evasion are any indication, UV stealth won't be quick, easy or cheap to develop.