Good question, judging by the responses :-)
From my research on my fathers AG service, his ship (the USAT Gen. George W. Goethals) left New York in early April 1944 for the UK. They spent nearly 2 months shuttling army troops from Belfast to various ports in England in preparation for D-Day, then another six weeks delivering troops to Omaha Beach and other areas in France. They returned back in Boston in late July 1944, and still had received no mail since leaving New York 3 months earlier.
Even though they were in "friendly" waters (to the extent that anything in the North Atlantic was friendly at that time) most of that time, no mail got through. This apparently had morale pretty low, so much so that the Armed Guard commander in his voyage report for that trip recommended to the Chief of Naval Operations that the CNO "secure closer cooperation between the U.S. Army which directs our movements and the Fleet Post Office."
I am sure that with the added stress and anxiety that came with the preparations for D-Day, these guys would have loved to have had a letter from home before going into harms way.
Happy to see some dialog from everyone. Be nice to hear from some new voices as well.