In 1926, three new ships joined the "US Sea Post" service.
They were given postmarks with the ship's name in the CDS and a number in the killer, as before:
- No. 6 - MINNEKAHDA 1926 to 1930
- No. 10 - LEVIATHAN (Ex VATERLAND) 1926 to 1928
- No. 15 - REPUBLIC 1927 to 17. August 1931
The ships "MINNEKAHDA" and "LEVIATHAN" also sailed in the joint service of the "US German Sea Post".
The "S.S. LEVIATHAN", as the largest ship in the world, was so popular with German and American passengers,
which resulted in a high volume of letters being mailed on board. Therefore, a
Stamping machine was installed with two postmarks, one for the eastbound route (Type 15) and one for the westbound route (Type 15A)(see illustration).
To Cockrill, Booklet No. 54
The "LEVIATHAN" was taken out of service from August 1933 to June 1934, after which she made only five round trips
and was then taken out of service again due to the "Great Depression" and finally laid up in September 1934.
Cockrill, Booklett No 54
Hosking, Seaposts of the USA
Overstamped domestic postcard with postmark type A14 to Cockrill with the number 6 in the killer. Postmarked April 23, 1928 aboard the steamer "MINNEKAHDA." Addressed to Middleport, N.Y.
Foreign postcard franked as required with postmark type A14 to Cockrill with the number 15 in the killer. Postmarked July 10, 1927 aboard the steamer "REPUBLIC". Addressed to Brazil.
As required franked domestic cover, collector's cover, with machine cancel type 15 to Cockrill with number 10 in the CDS. Postmarked on 01 August 1927 aboard the steamer "LEVIATHAN". Addressed to Washington, D.C.