Derek - Ha!  I don't think he ever jumped a fence fleeing the Germans. He'd certainly have shared that story with me!  However, he actually did own a 1953 Triumph while in Europe, as well.  I've got registration paperwork but no photos of that bike.  He bought the Triumph in 1956 for $200 USD. Chassis number was 38829.  Finding that actual bike (if it still exists) would be and epic feat!  Wish I had the chassis numbers on the BSA.  Cheers!

Dean - Thanks for the reply.  Unfortunately, he sold that bike before he returned to the US (and just a few years before I was born).  As such, I don't have any more detail on the bike (this photo and my moms stories are my only clues).  Dad passed many years ago so - again - not a lot to go on.  However, your insight is really helpful.  Now to see if I can count the number of fins from that photo!