An employee of the British Museum examines a silver coin dating from 900 AD which is part of the Silverdale Viking Hoard on December 14, 2011 in London, England. The hoard, which was discovered by local metal-detectorist Darren Webster in North Lancashire, comprises of 201 silver objects including arm-rings, coins, finger-rings, ingots, brooch fragments and fine wire braid. (Photo by Oli Scarff/Getty Images)

Dr. Christopher Brown (R), the Director of the Ashmolean, talks with Colin Harrison, the Ashmolean's Senior Curator of European Art, in front of a painting by Edouard Manet entitled “Portrait of Mademoiselle Claus” from 1868 in the Ashmolean Museum on February 24, 2012 in Oxford, England. The painting has been sold to a foreign buyer for 28.35 million GBP, however the Government has extended a temporary export bar on the artwork until August to give the Ashmolean an opportunity to raise funds to retain the painting in the UK. (Photo by Oli Scarff/Getty Images)

South Korean teenagers participate in a warfare exercise as part of the Special Warfare Command's training course at a military base on August 4, 2011 in Seoul, South Korea. About 1,000 civilian volunteers including middle and high school students participated in the special force's four-day training programme to develop their spiritual and physical strength. (Photo by Chung Sung-Jun/Getty Images)

Russian servicemen stand next to a Russian Yars RS-24 intercontinental ballistic missile system before a rehearsal for the Victory Day parade, with the Moscow International Business Center also known as “Moskva-City” seen in the background, at a range in Moscow, Russia, May 5, 2016. (Photo by Maxim Shemetov/Reuters)

Members of the local Cossack community undergo military training at a boot camp set up by the Russkiye Vityazi (Russian Knights) military patriotic club in the village of Sengileyevskoye, south of Stavropol, March 22, 2015. A group of cossacks from the village of Kazanskaya, who are planning a professional career at the military intelligence service, has arrived at a camp for training under the leadership of professional instructors. (Photo by Eduard Korniyenko/Reuters)

Russian President Vladimir Putin, center, uses a binocular, as Defense Minister Sergei Shoigu, left, and chief of Russia's military's General Staff Valery Gerasimov, right, observe military exercises near the Baikal Lake on Wednesday, July 17, 2013. (Photo by Alexei Nikolsky/AP Photo/RIA Novosti/Presidential Press Service)

Members of the Communist New Fourth Army on parade. Note how the modern equipment contrasts with the shoeless soldiers in the foreground. (Photo by Hulton Archive/Getty Images). 6th July 1946

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