A Palestinian boy takes part in a military-style summer camp being held by the Islamic Jihad movement during the youngsters' summer school vacation in Khan Younes town, in the southern Gaza Strip, 13 July 2016. Thousands of youngsters between the age of six and 16 can participate in the summer camp where they receive military as well as religious training. (Photo by Hatem Omar/EPA)

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)

A serviceman kisses the main icon for the Russian Armed Forces' main cathedral, delivered at the Church of Our Lady the Healer in Rostov-On-Don, Russia on May 15, 2018. The Russian Armed Forces' main cathedral is to be built in Patriot Military Park in Kubinka outside Moscow by 2020, the year of the 75th anniversary of the victory of the Soviet Red Army over Nazi Germany in the 1941-45 Great Patriotic War, the Eastern Front of World War II. (Photo by Valery Matytsin/TASS)

Students of the General Yermolov Cadet School take part in combined military training with members of a local youth military patriotic club at a boot camp of the Russkiye Vityazi (Russian Knights) military patriotic club in the village of Sengileyevskoye outside Stavropol, Russia February 8, 2017. (Photo by Eduard Korniyenko/Reuters)

NFL player Rob Gronkowski, of the New England Patriots, from second left, accepts the best comeback athlete award with his brothers, NFL free agent Chris Gronkowski and former NFL player Dan Gronkowski at the ESPY Awards at the Microsoft Theater on Wednesday, July 15, 2015, in Los Angeles. (Photo by Chris Pizzello/Invision/AP Photo)

Russian President Vladimir Putin aims a sniper rifle during a visit to the Patriot military exhibition center outside Moscow, Russia, Wednesday, September 19, 2018. Putin chaired a meeting that focused on new arms programs. (Photo by Alexei Nikolsky/Sputnik/Kremlin Pool Photo via AP Photo)

Mil Mi-8 combat helicopter flies over Moscow, Russia on May 7, 2019 during the dress rehearsal of a Victory Day air show marking the 74th anniversary of the victory over Nazi Germany in the 1941-1945 Great Patriotic War, the Eastern Front of World War II. (Photo by Sergei Savostyanov/TASS)