Also a big reminder of just how far we've come as I sit here about to communicate with the entire world almost instantly.
Finally, it also reminds me of one of my favorite RFCs, "IP over Avian Carriers with Quality of Service": https://tools.ietf.org/html/rfc2549
At this point in the war, all mail (not just those to service members) entering and exiting the United States were opened by hand and microfilmed for censorship and counter-espionage purposes by the Office of Censorship.
So technically the mail opening and scanning aren't extra overheads, since those same steps apply to regular snail mail as well.
My dad used to write letters and QSL cards to people all over the world in the 60s/70s. He recalled that frequently letters to soviet bloc states, northern ireland, and some african countries were opened, either by the US or other country.