Who is P.J.?

My mom and I found these in a bag of my grandma's old photos. Nobody can figure out who P.J. was, but he had a lovely, kind of bubbly script.

all aboard for Tokyo!
Syl, remember the 163rd St Crosstown?
P.J. April 1945

I presume the "Syl" was my grandma, but then again, in that generation there was at least one Sylvia in every Jewish household. I don't think P.J. is a relative of mine. I'm not sure where this photo was taken but I'm thinking he was probably shipping out from somewhere in California and was definitely not on a train on Honshu.

at ease!
P.J. May 1945

You can see the Army helmet on the right side of the photo. P.J. probably didn't have long to wait to go home.