Recruits with Delta Company, 1st Recruit Training Battalion maneuver through mud and barbed wire during the Combat Endurance Course on Dec. 21, 2019, at Marine Corps Recruit Depot Parris Island, S.C. (Gunnery Sgt. Tyler Hlavac/Marine Corps)
Tech. Sgt. Joshua Nordeen, a Pennsylvania Air National Guardsman, deices an aircraft early in the morning as the sun rises in Pittsburgh, Pa., on Dec. 12, 2019. (Staff Sgt. Bryan Hoover/Pennsylvania Air National Guard)
Santa Claus waves as he arrives in a 169th Fighter Wing F-16 Fighting Falcon at McEntire Joint National Guard Base, S.C., Dec. 7, 2019. (Staff Sgt. Megan Floyd/Air National Guard)
Guests attend a memorial service in the National Naval Aviation Museum at Naval Air Station Pensacola, Fla., on Dec. 19, 2019. The service was held for Ensign Joshua K. Watson, Naval Air Crewman (Mechanical) 3rd Class Mohammed S. Haitham, and Naval Air Crewman (Mechanical) 3rd Class Cameron S. Walters, who were killed during the Dec. 6, 2019, active-shooter incident. (Chief Mass Communication Specialist David Holmes/Navy)
A member of the U.S. Air Force holds up a full-field American flag as it is displayed on the field before the Mitsubishi Motors Las Vegas Bowl between the Washington Huskies and the Boise State Broncos at Sam Boyd Stadium on Dec. 21, 2019 in Las Vegas. (David Becker/Getty Images)
An F/A-18E Super Hornet launches from the flight deck of the aircraft carrier USS Theodore Roosevelt (CVN 71) on Dec. 12, 2019, in the Pacific Ocean. (Mass Communication Specialist 2nd Class Pyoung K. Yi/Navy)
A U.S. Army paratrooper lands at Alzey drop zone Dec. 18, 2019, after jumping off a C-160 during Operation Toy Drop 2019, at Alzey, Germany. (Staff Sgt. Sinthia Rosario/Army)
U.S. Army soldiers and multinational partners walk to the rendezvous point during Operation Toy Drop near the town of Alzey, Germany, on Dec. 18, 2019. (Ismael Ortega/Army)
Cpl. Rayfel Gonzalez digs an entrenchment for an M240B machine gun Dec. 11, 2019, during exercise Steel Knight 20 (SK20) on Marine Air-Ground Combat Center, Twentynine Palms, Calif. (Cpl. Sabrina Candiaflores/Marine Corps)
An MH-60S Sea Hawk helicopter transports cargo to the aircraft carrier USS Harry S. Truman (CVN 75) from the USNS Wally Schirra (T-AKE 8) during a replenishment-at-sea in the Arabian Sea on Dec. 21, 2019. (Mass Communication Specialist 2nd Class Jake Carrillo/Navy)
