Something a little different which may generate some interest
Scans show a cover sent Free to Bureau International de la Piax, Berne, Switzerland from a German POW, No 20753 in No 2 POW Hospital, Heliopolis, Egypt
Framed FREE and unframed FROM PRISONER OF WAR Cachets
Censor 3 / 3282 applied in Egypt. Cover went via CONSTANTINOPLE and was received in Berne 30 April 1918
Route via Constantinople seems a little strange, however first I've seen of a German POW in Egypt writing to Berne.
Chris