The U.S. drone war across much of the Greater Middle East and parts of Africa is in crisis and not because civilians are dying or the target list for that war or the right to wage it just about anywhere on the planet are in question in Washington. Something far more basic is at stake: drone pilots are quitting in record numbers.

There are roughly 1,000 such drone pilots, known in the trade as “18Xs,” working for the U.S. Air Force today. Another 180 pilots graduate annually from a training program that takes about a year to complete at Holloman and Randolph Air Force bases in, respectively, New Mexico and Texas. As it happens, in those same 12 months, about 240 trained pilots quit and the Air Force is at a loss to explain the phenomenon. (The better-known U.S. Central Intelligence Agency drone assassination program is also flown by Air Force pilots loaned out for the covert missions.)

On January 4, 2015, the Daily Beast revealed an undated internal memo to Air Force Chief of Staff General Mark Welsh from General Herbert “Hawk” Carlisle stating that pilot “outflow increases will damage the readiness and combat capability of the MQ-1/9 [Predator and Reaper] enterprise for years to come” and added that he was “extremely concerned.” Eleven days later, the issue got top billing at a special high-level briefing on the state of the Air Force. Secretary of the Air Force Deborah Lee James joined Welsh to address the matter. “This is a force that is under significant stress — significant stress from what is an unrelenting pace of operations,” she told the media.