A line of soldiers firing handguns during a training session, circa 1920. (Photo by Keystone). P.S. All pictures are presented in high resolution.

Three Chinese soldiers at the time of a civil war in China. (Photo by General Photographic Agency/Getty Images). 1922

Soldiers take part in a drill during a heavy snow in Heihe, Heilongjiang province, February 26, 2014. (Photo by Reuters/China Daily)

A Saudi soldier fires a mortar towards Houthi movement position, at the Saudi border with Yemen April 21, 2015. (Photo by Reuters/Stringer)

A soldier helps another with her ear protection at the Terningmoen Camp in Elverum, Norway on March 23, 2017. Soldiers demonstrate their skills and tactics during a contract drill as they train to become part of the world's first all-female special forces unit, the Jegertroppen or “hunter troops”. (Photo by Carolina Reid/NBC News)

A parrot stuck on a roof for three days greeted firefighters sent to its aid on August 13, 2018 with a four-letter tirade. Jessie, the multi-lingual Macaw, flipped the bird after escaping from her owner's home in Edmonton, north London, UK. When she could not be lured down from a neighbour's roof, firefighters were called out and told to tell the bird “I love you” – to which Jessie replied “I love you back”. But she then ruffled her would-be rescuers' feathers by telling them to “f**k off” before flying off to another nearby rooftop. The foul-mouthed pet also speaks Turkish and Greek according to its owner, but had its own choice words in English for the rescue team. As Jessie wasn't injured, the firefighters, who had been called in by the RSPCA, left her on her perch. The parrot was later reunited with its owner. (Photo by Rex Features/Shutterstock)

Russian soldiers write home while serving on the Eastern Front during World War I, circa 1915. (Photo by Hulton Archive/Getty Images)

Israeli soldiers get ready to launch the Skylark drone during a drill on January 16, 2012 near Bat Shlomo, Israel. (Photo by Uriel Sinai/Getty Images)