9. A Royal Mail Ship
The R.M.S. Titanic was a Royal Mail Ship, a designation which meant the Titanic was officially responsible for delivering mail for the British postal service.
On board the Titanic was a Sea Post Office with five mail clerks (two British and three American).
These mail clerks were responsible for the 3,423 sacks of mail (seven million individual pieces of mail) on board the Titanic.
Interestingly, although no mail has yet been recovered from the wreck of the Titanic, if it were, the U.S. Postal Service would still try to deliver it (the USPS because most of the mail was being sent to the U.S.).