This photo provided by Running Press and Quarto, Inc. shows Feline Fox from the book, “Cats in Hats”, published by Running Press. The book released on March 24, 2015. (Photo by Liz Coleman/Running Press/Quarto, Inc. via AP Photo)

German flying ace Baron Manfred von Richthofen (1892–1918) also known as The Red Baron with his dog Moritz, circa 1916.

A German special anti-tank gun is ready to fire during the army maneuvers in Silesia, Poland, on September 22, 1928. (Photo by AP Photo)

Colorado Gov. John Hickenlooper shows off his socks--one with Democratic presidential candidate Bernie Sanders and the other with Republican candidate Donald Trump – before entering his former brewpub for a book signing event to mark the release of his autobiography Thursday, May 26, 2016, in Denver. Hickenlooper, who is term-limited, is doing book talk rounds this week, reviving speculation that he is positioning himself to join Hillary Clinton's presidential campaign ticket. (Photo by David Zalubowski/AP Photo)

A German rifleman beside the corpse of a French soldier in a trench at Fort Vaux, France, 1916. (Photo by Hulton Archive/Getty Images)

A dejected German Grenadier carrying a machine gun on his shoulder in front of a building on fire during the German retreat in Russia. (Photo by Keystone/Getty Images). 1944

German police officers take pictures as fireworks explode next to the Quadriga sculpture atop the Brandenburg gate during New Year celebrations in Berlin, Germany, January 1, 2017. (Photo by Fabrizio Bensch/Reuters)