The British Library website has a number of images devoted to Walter Flex from the Staatsbibliothek zu Berlin. The most moving are a series of photographs of the map that was in Flex’s possession when he was fatally shot with the bullet hole clear to see:

Trees, swampland, lakes, villages and cottages are all marked on this map of the Baltic island Saaremaa, offshore from Estonia and at the time under Russia. Flex and his division had landed in October 1917 and after three days of struggling, the Russians surrendered their arms. All but one soldier surrendered their arms: the remaining man refused and shot Flex down. The bullet tore his right forefinger off, entered his body and became lodged near his stomach. He wrote a last line: ‘Dear parents! I dictate this postcard as I’m slightly wounded at the forefinger of my right hand. Besides this, I am well off. There’s no room for worry whatsoever. Love, Walter.’ He died the next day, aged just 30, due to his internal injuries.