It was really neat to discover this forum. My Grandfather served in UDT-4 during WW-II and he is in some of the above pictures. His name was Frank Zajac. Here is one of his pictures from WW-II, Grandpa Frank is on the left. I don;'t know the other two guys in the picture, if anyone could identify them I would appreciate it.
Paul, glad you found this forum and pics of UDT-4!
The gentleman in the middle is Mr. Wood... and on the right is "Swede" (not sure of his name but this is what he was called).
According to Tom Hannigan, your grandfather was given the nickname of "Primo". I'll have to go thru the photos he gave me, I think there may be more pics of your grandfather. I'll pull them out and post them. If you scroll back up thru the pics I posted, you'll see your grandfather in a few of them - his name noted as "Primo".
P.S. I knew a Paul Zajac in south Florida quite a few years back.... any relation?