U.S. soldiers take part in the Ranger Course on Fort Benning, Ga., April 21, 2015. (Paul Sale/U.S. Army)

Cpl. James Kanal, in red, a paratrooper assigned to the 82nd Airborne Division, delivers a punch to Pvt. Tom Barry, a paratrooper from 3rd Battalion The Parachute Regiment, during a preliminary fight at the International Paratrooper Brawl held at Ritz Epps Gym on Fort Bragg, N.C., April 23, 2015. (Eliverto V. Larios/U.S. Army)

Members of the Army National Guard's 20th Special Forces Group (Airborne) enter the water at Naval Station Mayport, Fla., on April 29, 2015. (Adam Fischman/U.S. Army)

Spc. Samantha B. Desrosier, with the 485th Engineer Company, smooths mortar to prevent water from collecting in the pores for a classroom wall during a civic and medical assistance mission to El Salvador. (Lindsey A. Schulte/U.S. Army)

Belgian Army soldiers conduct a reconnaissance and surveillance mission during exercise Saber Junction 15 at the U.S. Army?s Joint Multinational Readiness Center in Hohenfels, Germany, April 23, 2015. (Markus Rauchenberger/U.S. Army)

After a productive week of mandatory training, the 81st Regional Support Command ended its annual training by participating in a teamwork development course at Fort Jackson, S.C., April 24, 2015. (Kandi Huggins/U.S. Army)

An Iraqi army soldier with the 73rd Brigade, 15th Division, tosses a simulated grenade into a bunker during a cumulative training event at Camp Taji, Iraq, April 16, 2015. U.S. paratroopers with 5th Squadron, 73rd Cavalry Regiment, 3rd Brigade Combat Team, 82nd Airborne Division, were the primary trainers during the course and provided minimal instruction during the final event. (Cody Quinn/U.S. Army)

Iraqi army soldiers with the 73rd Brigade, 15th Division, provide cover fire for their platoonmates while a U.S. soldier, left, with 5th Squadron, 73rd Cavalry Regiment, 3rd Brigade Combat Team, 82nd Airborne Division, demonstrates how to aim properly during a cumulative training event at Camp Taji, Iraq, April 16, 2015. (Cody Quinn/U.S. Army)

M1A2 Abrams tanks of 1st Battalion, 66th Armor Regiment, 3rd Armored Brigade Combat Team, 4th Infantry Division are prepared to begin Gunnery Live Fire Qualifications at the Udairi Range Complex, Kuwait, April 26, 2015. (Shaun Manley/U.S. Army)

Soldiers of 1st Infantry Brigade, Estonian Defense Force, prepare their Pvpj 1110 Recoilless Rifle for a third fire after successfully destroying two HMMWVs of Anvil Troop 1st Squadron, 91st Cavalry Regiment, 173rd Airborne Brigade during a notional firefight as part of Field Training Exercise Hunt April 26, 2015, at the Central Training Area, Estonia. (Joshua S. Brandenburg/U.S. Army)

An aviator from the 1st Battalion, 52nd Aviation Regiment stands outside a CH-47F Chinook helicopter at the Kahiltna Glacier base camp on Mount McKinley in the shadow of 13,965-foot Mount Hunter on April 27, 2015. (John Pennell/U.S. Army)