This required some math on my part because both Sam and Friedrich had to be of an age where they could have served in WWI (the book is set in 1925 Berlin). Friedrich is perhaps a touch young to have made colonel by the time he was decommissioned, but he comes from a military family and I figure he’d have had at least one battlefield promotion during the war. Sam would have joined up at the urging of his boyfriend and Katherine’s brother Bart, back when young American men thought it would have been a rousing adventure to go and fight the Hun. They had no idea the hell they were letting themselves in for.