A member of the Eton public school O.T.C. (Officers Training Corps) practising shouting out orders during a training session, 20th January 1940. (Photo by Hulton Archive/Getty Images)

Afghanistan's interior ministry special forces demonstrate their skills during a military exercise in Kabul, Afghanistan, Thursday, April 2, 2015. Afghanistan's security forces took over full responsibility for the country's security on January 1, 2015. (Photo by Massoud Hossaini/AP Photo)

Tech. Sgt. Milo Hinson, 3rd Combat Camera Squadron, uses a flashlight while shooting a Berretta 9mm during the night-fire portion of Advance Weapons, Tactics and Techniques training in San Antonio. During night-fire training, airmen learn how to tactically illuminate targets with flashlights and practice using night vision goggles. (Photo by Staff Sgt. Jonathan Snyder/U.S. Air Force). 2011

A South Sudanese People Liberation Army (SPLA) soldier patrols the streets in Malakal on January 21, 2014. (Photo by Harrison Ngethi/AFP Photo)

A woman walks against blowing snow in Evanston, Illinois, on February 8, 2014. (Photo by Nam Y. Huh/Associated Press)

The Euro sculpture is partially reflected in a puddle on a cobblestone pavement in front of the headquarters of the European Central Bank in Frankfurt on Jan. 21. (Kai Pfaffenbach/Reuters)

The hot air balloon “Hopper T Frog” from Park City, Utah, peeks over the red rock cliffs during the 23nd Annual Red Rock Balloon Rally at Red Rock State Park December 6, 2003 near Gallup, New Mexico. (Photo By Douglas Tesner/Getty Images)

Two men fight in San Jose, Costa Rica, during the Women's Day on March 8, 2014. (Photo by Jeffrey Arguedas/EFE/SIPA Press)