The Pentagon’s favorite new drone for airstrikes and monitoring militant terrorist groups is falling out of the sky at an alarming rate, thanks to an overload of mysterious electrical failures.

Accident reports obtained through a Freedom of Information Act request about the advanced Reaper “hunter-killer” drone show it fell victim to a faulty-starter generator, but investigators are unsure what’s causing the problem or how to fix it.

A total of 20 large Air Force drones were destroyed or damaged to the tune of $2 million in accidents in 2015, at least half of which were Reapers. This is horrible timing, as field commanders increasingly rely on drones for counterterrorism operations, with Air Force officials now offering a retention bonus of $125,000 just to keep its overloaded drone pilots. That’s a drop in the bucket compared to the roughly $14 million cost of replacing a 2.5 ton Reaper drone, even as the model’s 2015 rate of major crashes over 100,000 hours doubled from 2014.

Despite the problems, the Air Force is investing in dozens of new Reapers over the next few years. The move is part of a broader military trend of increased drone reliance, from building cheaper and disposable “Gremlin” drones to invisible stealth models.

Both the Reaper and Predator drones are built by the San Diego-based General Atomics Aeronautical Systems. The defense contractor declined to comment to Inverse regarding the findings by the Washington Post, which submitted the Freedom of Information Act request. In the Post’s investigation, company spokesperson Kimberly Kasitz was quoted as saying General Atomics “stands behind” their product’s “proven reliability.” It should be noted that the Predator, an older, less refined model of the Reaper, is falling down on the job nearly as often, also crashing at least 10 times in the last year.

The systematic failure of literally hundreds of millions of dollars in military would be bad enough, but it looks like the Air Force has tried to sweep this under the rug as much as possible, noting to the Post:

Although the Defense Department has a policy to disclose all major aircraft mishaps, it did not publicly report half of the 20 Reaper and Predator accidents last year.

In five other cases, U.S. military officials provided confirmation only after local authorities reported the crashes or enemy fighters posted photos of the wreckage on social media.

Photos via Getty