Senior Airman Cullen Thomas, 824th Expeditionary Base Defense Squadron military working dog handler, and his military working dog Klepa perform a perimeter check at Nigérien Air Base 201, Niger, Dec. 9, 2018. (Staff Sgt. Daniel Asselta/Air Force)
Airman 1st Class Ashley Libby, a 99th Medical Operations Squadron aerospace medical technician at Nellis Air Force Base, Nev., raises her arms to keep the American flag off the ground during the 2018 Las Vegas Bowl opening ceremony at Sam Boyd Stadium in Las Vegas, Dec. 15, 2018. The half-ton flag required more than 200 airmen to carry it. (Senior Airman Andrew D. Sarver/Air Force)
A Marine tests the fit of his M50 Joint Service General Purpose Mask outside the gas chamber at Camp Hansen, Okinawa, Japan, Dec. 19, 2018. (Lance Cpl. Andrew R. Bray/Marine Corps)
Members of Battery C, 1st Battalion, 9th Field Artillery Regiment fire a salute Dec. 21, 2018, in honor of the Georgia National Guard's 48th Infantry Brigade Combat Team, which held a casing ceremony at Fort Stewart, Ga. This is the fourth combat deployment of the 48th IBCT since Sept. 11, 2001. (Maj. William Carraway/Army)
An MH-60R Sea Hawk helicopter takes off from the flight deck of the aircraft carrier USS John C. Stennis (CVN 74) during a transit through the Strait of Hormuz on Dec. 21, 2018. (MC3 Grant G. Grady/Navy)
Army Spc. Kaleb Steffens, gunner, Delta Company, 4th Platoon, 1st Battalion 141st Infantry Regiment, Task Force Alamo, Texas National Guard, deployed to Combined Joint Task Force-Horn of Africa, Djibouti, fires a .50-caliber Common Remotely Operated Weapon Station on top of a Mine-Resistant Ambush-Protected vehicle during training at a military range in Djibouti, Dec. 15, 2018. (Tech. Sgt. Shawn Nickel/Air Force)
MV-22 Ospreys prepare to launch from the flight deck of the Wasp-class amphibious assault ship USS Kearsarge (LHD 3) on Dec. 23, 2018, during night flight operations in the Atlantic. (MC1 Mike DiMestico/Navy)
Marines and sailors with Special Purpose Marine Air-Ground Task Force stand at attention before Commandant of the Marine Corps Gen. Robert B. Neller speaks in Sigonella, Italy, Dec. 25, 2018. (Sgt. Olivia G. Ortiz/Marine Corps)
A B-1B Lancer and a KC-135 Stratotanker conduct aerial refueling over the continental United States on Dec. 10, 2018. (Staff Sgt. Joshua Williams/Air Force)
Hull Maintenance Technician 3rd Class Sikeston Bingham stands watch on the flight deck aboard the Nimitz-class aircraft carrier USS Harry S. Truman (CVN 75) on Dec. 20, 2018, at Naval Station Norfolk. (MC3 Joseph A.D. Phillips/Navy)