After seeing your message, I found my dad's 421 FA B book, and found Robert Rivas listed, with a Los Vegas address. From skimming the book, I know they were on Okinawa and May 1945 sounds about right. I will see if I can locate a picture or more info. The book contains a good history of the unit's formation, duties and such. Other than that a lot of pictures with no index so finding an individual is a little tough. From a quick skim, it seems like the unit was initially anti aircraft in the LA area protecting the airplane factories. At some point they were shipped to Ft. Sill for training in rocket launchers, sent to Washington state and shipped to Okinawa. I don't recall anything about Ft. Bliss Chances are they knew each other. I remember my dad telling me (and the book confirming) that when the unit was first formed, it included a Nevada National Guard unit so he knew a number of people from that state.