Larger type US Naval vessels have a fully operational post office aboard including destroyers. However, the post office aboard most destroyers was a very small space that typically had only one person supporting it at a time. This Post Office would undertake the handling of all US Mail being shipped out and brought aboard for the crew. Thousands of packages, letters, and other correspondence were processed via this small office with every letter going out being stamped with the ship's Post Mark stating the date and ship name.
For sailors away at sea for months at a time, this was the only contact they had with home and they saw the mail service as a very important activity aboard the ship. Mail for destroyers would be transferred via helicopter or high-line transfer at sea for all exchanges. Mail would then be sorted and readied for the crew. The ship's postal clerk would also process money order's for crewmembers who wished to have them made up to send money home or elsewhere.