Actually, the story of Rin-Tin-Tin's birth on a battlefield in September of 1919 very likely is myth. The first story that Duncan told (in October, 1919, to the Los Angeles Times) and that three officers of his squadron told goes like this: Duncan and his mates found an adult German shepherd male on the battlefield, and Rin-Tin-Tin was one of a litter born to him and a female German shepherd. That means he was born around the time of the Armistice. Evidence shows that story to be the true one. In a photograph taken after the 135th Aero Squadron arrived back in the United States in May, 1919, Duncan sits on the ground with Rin-Tin-Tin in his arms; next to him is another man with Nanette, Rin-Tin-Tin's sister. Rin-Tin-Tin's ears are floppy; Nanette's stand straight up. German shepherd puppies' ears start to stand up when they are five or six months old. (That's also the age the puppies appear to be, not the nine months they would have been had they been born in September.)
I am a historian. See my book, Rin-Tin-Tin: The Movie Star, available on Amazon.