United States Mail Ship, usually abbreviated to USMS or USM, is a ship prefix used for seagoing vessels that carry mail under contract with the United States Postal Service. It was used sporadically by many shipping lines, but is often associated in particular with the U.S. Mail Steamship Company, Collins Line, and American Line which held a number of high-profile mail contracts, and traditionally prefixed the names of many of their ships with the initials "USM" or "USMS".
List of past United States Mail Ships This is an incomplete list, you can help by expanding it.
See also Royal Mail Ship
References