SS Tregarthen was a cargo steamship that was built in Scotland for the Hain Steam Ship Co in 1936.

[2] In 1936 Lithgows built a pair of steamships in its Port Glasgow shipyard for the Hain SS Co. Trewellard was launched on 16 June 1936 and completed that July.

[8] She returned to Britain that May carrying iron ore.[9] In July 1940 she took coal from Canada to Reykjavík in Canadian-occupied Iceland.

[10] Tregarthen made each of her eastbound Atlantic crossings with the protection of an HX convoy from Halifax, Nova Scotia to Britain.

[11] Tregarthen began most of her westbound Atlantic crossings with the protection of an OB (Outward Bound) convoy.