Gremlins were not "luck charms of many British pilots during World War II" as Darpa states. They were bad luck demons that could kill pilots.

"Gremlins were said to engage in such a myriad of bad behavior as sucking the gas out of tanks through hoses, jamming radio frequencies, mucking up landing gear, blowing dust or sand into fuel pipes or sensitive electrical equipment, cutting wires, removing bolts or screws, tinkering with dials, knobs or switches, jostling controls, slashing wings or tires, poking or pinching gunners or pilots, banging incessantly on the fuselage, breaking windows, and a wide variety of other prankish acts. "

https://mysteriousuniverse.org/2015/07/the-real-gremlins-of-...