Seapost -> United States Sea Posts
United States Sea Posts
By Roger Hosking

This envelope was posted from the 4th sailing of the SS New York using the new US Seapost cancel and could be the earliest known posting, dated May 20th 1893
Although the seapost routes operated by the US Post Office are by no means as numerous or widespread as those of their French and German counterparts, their cancellations (applied to passenger mail), and their ancillary markings (on mail sorted in transit), still provide an interesting field of study. The service began in 1891 and ended in 1942, i.e. just after the American declaration of war in December 1941. There are four main geographical groupings, as follows:-

1. Transatlantic (1891-1939). This comprised a purely US service, and also joint services with the German, British, and French post offices, the last two being rather short-lived. Routes were from New York to Hamburg/Bremen, Liverpool/Plymouth/Southampton, and Le Havre/Bordeaux. [See also British Transatlantic Sea Post Offices, German Sea Post Offices on German and American Ships and French Sea Posts.]

2. Transpacific (1922-1939). An all-American effort, with routes from San Francisco / Seattle to Hong Kong / Manila numbered from 1 to 4.

3. Central America, with routes from New York to Porto Rico (1912-1942), and from New York to the Canal Zone (1907-1932).

4. South America, with routes from New York to Valparaiso (1928-1941), and from New York to Buenos Aires (1926-1941) from a number of different vessels.

This cover was posted on the Atlantic route from the SS Leviathan in 1927 with a number 10 in the postmark. It was used from 1927 until 1934.
The following cover illustrates an interesting use of U S Post Office Official Seals to close an envelope found open while sorting on board the U S Line's 'Philadelphia'. This cover originated in New York but was not cancelled prior to being put on board.

The manuscript notation reads "Received unsealed/Sea Post #2". The back is sealed with Official Seals [Scott OX13 (2) & Sc OX13e pair on toned paper]. There is a Danish backstamp and more 'United States * Sea P.O. * / 2' marks.

Cover courtesy Stephen Taylor.
Instructions for the Conduct of Sea Post-Offices
Click this link to read about the procedures governing the joint USA - German and USA - British sea post offices, how the crew made up bags of mail for the German TPOs, and the order of distributing the bags at Plymouth, Bremen and Hamburg.
References:
The following will be found very useful:
Seaposts of the USA, by Roger Hosking, TPO & Seapost Society, 2008, ISBN No 978-0-9518726-6-6
The Transatlantic Post Office, by Roger Hosking, Oxted, June 1979.
United States Sea Post Cancellations Part I Transatlantic Routes, P Cockrill, Cockrill Series
Booklet No 54. ISBN No 947628 59 2
Scott Specialized Catalogue of US Stamps and Covers, Scott Publishing Co., Sidney, OH 45365-0828