Air Force

FILE - In this April 9, 2018, file photo, Deputy Secretary of Defense Patrick Shanahan, right, listen as President Donald Trump speaks during a cabinet meeting at the White House, in Washington. A U.S. administration official says that Defense Secretary Jim Mattis will leave his post Jan. 1, 2019, as Trump is expected to name Shanahan as acting secretary. (AP Photo/Evan Vucci, File)

FILE – In this Dec. 24, 2017, file photo, Canadian Lt. Maj. Chris Hache takes a call while volunteering at the NORAD Tracks Santa center at Peterson Air Force Base in Colorado Springs, Colo. Hundreds of volunteers will help answer the phones again when the program resumes on Monday, Dec. 24, 2018, for the 63rd year. Children from around the world call to ask when Santa Claus will get to their house. (Jerilee Bennett/The Gazette via AP, File)

President Donald Trump, right, talks with Army Chief of Staff Gen. Mark Milley, left, during the Army-Navy NCAA college football game in Philadelphia, Saturday, Dec. 8, 2018. Trump announced that Milley will be the next chairman of the Joint Chiefs of Staff. (AP Photo/Susan Walsh)

Students from Salyer Elementary School wave flags as the train carrying the body of former president George H.W. Bush travels past their school on the way to Bush's final internment Thursday, Dec. 6, 2018, in Spring, Texas. (AP Photo/Michael Wyke)

FILE - In this July 10, 2017, file image made from video provided by WLBT-TV, smoke and flames rise from a military plane that crashed in a farm field in Itta Bena, Miss. Investigators say bad maintenance practices at a Georgia air force base missed a deteriorating propeller blade that broke off six years later as a U.S. Marine Corps transport plane cruised over Mississippi at 20,000 feet, causing the KC-130T to break into pieces and plunge into a soybean field, killing 15 Marines and a Navy corpsman, according to the report on the causes of the July 10, 2017, crash, released Wednesday, Dec. 5, 2018. (WLBT-TV via AP, File)

President Donald Trump speaks to media about the death of former President George H. W. Bush, during his meeting with Germany's Chancellor Angela Merkel at the G20 summit, Saturday, Dec. 1, 2018, in Buenos Aires, Argentina. (AP Photo/Pablo Martinez Monsivais)

President Donald Trump talks to a pilot in the cockpit of an F-35 aircraft during a Defense Capability Tour at Luke Air Force Base, Ariz., Friday, Oct. 19, 2018. (AP Photo/Carolyn Kaster)