The Air Force's protracted personnel shortage has been called a "quiet crisis."

The service has pursued a number of policy changes to keep pilots in uniform.

The Defense Department now has the authority to recall retired officers.

President Donald Trump amended an executive order on Friday to allow the Defense Department to recall up to 1,000 retired pilots in order to address the Air Force's shortage of qualified fliers.

Defense Secretary Jim Mattis reportedly requested the move, and he now has "additional authorities to recall retired aviation officers," Pentagon spokesman Navy Cmdr. Gary Ross said in a statement.

The Air Force is currently about 1,500 pilots shy of the 20,300 it is mandated to have. Of those missing, about 1,000 are fighter pilots. Some officials have deemed the shortage a "quiet crisis."

"We anticipate that the Secretary of Defense will delegate the authority to the Secretary of the Air Force to recall up to 1,000 retired pilots for up to three years," Ross said.

President Donald Trump meeting with US airmen and Air Force Chief of Staff Gen. David L. Goldfein at Joint Base Andrews, Maryland, September 15, 2017. (US Air Force photo by Scott M. Ash)

Executive order 13223 declared a temporary state of emergency after the September 11 attacks and allowed the president to call up the National Guard, hire and fire officers, and delay retirements. It has been renewed by every president since, including Trump, but under the previous version only 25 retired officers could to be called back to active duty. Trump's amendment expands that authority.

"The authorities available for use during a national emergency ... are also invoked and made available, according to their terms, to the Secretary concerned, subject in the case of the Secretaries of the Army, Navy, and Air Force, to the direction of the Secretary of Defense," the amended order reads.

The Air Force has played a central role in the US-led campaign against ISIS in Syria and Iraq, flying most of the combat sorties during the three-year-old effort. The intensity of the operations has placed additional demands on the Air Force's pilots and aircraft, which are also seeing more duties in Europe and Asia.

An air crew in an 816th Expeditionary Airlift Squadron C-17 Globemaster III loadmaster prepare for takeoff before a mission in support of Operation Inherent Resolve, at Al Udeid Air Base, Qatar, August 23, 2017. (US Air Force photo/Staff Sgt. Michael Battles)

Air Force officials have pointed to commercial airlines, which pay more, as the main draw for fliers; budget cuts, longer deployments, and long-term personnel drawdowns have also contributed to more pilots leaving. (The service is also dealing with a shortage of aircraft maintainers.)

The service is pursuing a bevy of changes to retain pilots and airmen, including more flexible assignment policies, increased pay and bonuses, and reshuffling of administrative duties. It is also looking to change its training programs, potentially outsourcing some elements in order to resolve a personnel bottleneck and free up Air Force aircraft for other uses.

In August, Air Force Secretary Heather Wilson announced the Voluntary Rated Return to Active Duty, or VRRAD, program, which allowed up to 25 retired qualified pilots to return to fill "critical-rated staff positions" so active-duty pilots could stay with units where they are needed to meet mission requirements.

Staff Sgt. Kevin Colon removes exhaust covers from a B-1B Lancer at Nellis Air Force Base, Nevada, May 21, 2013. U.S. Air Force

A general was picked to lead to the Air Force's aircrew crisis task force, which is focused on training and retaining pilots and resolving the shortage.

The service's budget request for 2018 also sought to balance "readiness recovery, strategy-based modernization, and acquisition programs."

At least one Air Force officer has mentioned "stop-loss" policies as a way to keep fliers in uniform.

The executive order the president signed on Friday is not limited ot the Air Force, and it could allow other branches to call up officers in the future.

Already the Air Force looks poised to take a greater role in Afghanistan as part of Trump's intensified campaign against the Taliban and other insurgents there.

After the killing of four US soldiers in Niger, US counterterror efforts look likely to expand around the world.

"The war is headed to Africa," Sen. Lindsey Graham said on Friday. "It's beginning to morph." Graham added that US targeting of terrorism suspects would become more aggressive and rules of engagement would be changed. "As we suppress the enemy in the Mid East, they're going to move," he said. "They're not going to quit."