The U.S. Air Force is more than doubling special pay for drone pilots to $1,500 a month -- a move designed to address a personnel shortage in the highly stressed workforce.

Air Force Secretary Deborah Lee James announced the service will increase monthly incentive pay for operators of so-called remotely piloted aircraft, or RPAs, from $600 a month to $1,500 a month.

"I just signed the memo earlier today," James said during a State of the Air Force briefing Thursday at the Pentagon, though she didn't specify how soon the additional money will be available for qualifying airmen.

Unlike pilots of manned aircraft, pilots of the service's MQ-1 Predator and MQ-9 Reaper drones aren't currently eligible for aviation continuation pay of as much as $25,000 a year. While officials are working to change that policy, James said as an interim solution she exercised her authority to offer the increased monthly incentive pay.

"We will also explore more permanent incentive plans," she said.

James said she made the decision after visiting with crews over the past year at Creech Air Force Base in Nevada, the service's headquarters for drone missions overseas, where she learned firsthand of the stresses facing the workforce.

Beyond pay, the service also plans to mobilize more members of the Air National Guard to help man active-duty RPA units, encourage airmen who volunteered to fly Predators and Reapers in the past to return to the units, and delay allowing pilots who are authorized to fly both manned and unmanned aircraft to leave the drone units.

The Defense Department planned to spend about $5 billion on unmanned systems in fiscal 2015, the vast majority for unmanned aerial systems, or UAVs, according to a report. The Pentagon has more than 200 Predators and more than 100 Reapers, which can also be used for strike missions and are made by General Atomics Aeronautical Systems Inc., based in San Diego.

The workforce has been stressed for years as commanders in Afghanistan and other combat zones demanded more intelligence, surveillance and reconnaissance from drones. The number of remotely piloted combat air patrols, or CAPs, more than doubled from 21 in 2008 to more than 55 today, according to Air Force Chief of Staff Gen. Mark Welsh.

"Our crew force will tell you, they enjoy the mission ... they're just worn out," he said during the briefing. "The crisis now is with the pilot force ... because we're reaching the point where some of them can go."

The Air Force currently trains about 380 remotely piloted aircraft operators a year, but loses about 240 of them due to attrition, Welsh said. Even the training units are chronically understaffed because many trainers are pulled from operational units, he said.

The service is considering following the Army in allowing non-commissioned officers fly unmanned aircraft, Welsh said. It’s looking at encouraging pilots from services that are divesting aviation assets to move into the RPA field, he said.

Neither Welsh nor James specified how much the retention effort might cost, but said it would have to be funded in an annual appropriation going forward.

"We have ... to get ahead of this," Welsh said.

-- Brendan McGarry can be reached at brendan.mcgarry@military.com