North Korean soldiers wave along the Yalu River, near the North Korean town of Sinuiju, opposite to the Chinese border city of Dandong October 7, 2014. (Photo by Jacky Chen/Reuters)

Members of an American landing party assist troops whose landing craft was sunk by enemy fire off Omaha beach, near Colleville sur Mer, France, June 6, 1944. REUTERS/Weintraub/US National Archives

Lightning illuminates a thundercloud as a storm front hits the North Sea region near Westerhever, northern Germany, on August 11, 2014. (Photo by Daniel Reinhardt/AFP Photo/DPA)

An enormous crocodile mauls a young hippo calf carcass near Lower Sabie on May 11, 2014, in Kruger National Park, South Africa. An enormous crocodile tosses around a young hippo calf caught in its lethal jaws. The giant reared out of the water revealing a young hippo calf between its teeth. The huge beast then span, jumped and splashed in the water with the small carcass. Amateur photographer Roland Ross captured these incredible photographs near Lower Sabie in Kruger Park, South Africa. (Photo by Roland Ross/Barcroft Media)

A makeshift cart with containers is seen at a suspected drug tunnel under construction during a media tour by Mexican Army in Tijuana April 7, 2015. Mexican soldiers foiled the construction of a suspected drug tunnel underneath a house near the U.S. border, arresting nine people and impounding a truck used to clear debris, the Army said on Tuesday. Wired with lights, the tunnel was being built next to the Tijuana border crossing, south of San Diego, California, and near a Mexican air force installation as well as a regional federal police facility. (Photo by Reuters/Stringer)

A member of a local swimming club holds a Russian national flag as he dives in at the start of a 24-hour swimming marathon near the western Siberian city of Barnaul March 29, 2014. Thirty members of the club will swim in turn during the event, held to mark Crimea becoming part of Russia, local media reported. (Photo by Andrei Kasprishin/Reuters)

U.S. Army soldiers with the 1st Battalion, 501st Infantry Regiment deployed to Combat Outpost Sabari, Afghanistan scan their area as they begin a multi-day air assault mission near the Pakistani border of eastern Afghanistan's Khost province May 2, 2012. (Photo by Staff Sgt. Joshua L. DeMotts/U.S. Air Force)