[1] The 3,477 GT Munamar, built by Maryland Steel in Baltimore,[2] became the first passenger liner and was employed on the eastern Cuba route.

[6] In July 1921, four Type 535 class ships—American Legion, Southern Cross, Pan America, and Western World—were assigned to the Munson Line by the USSB (and the former North German Lloyd ships were returned).

In 1931, Western World ran aground off the coast of Brazil, where she would remain for four months before finally arriving in New York for repairs.

But the Great Depression dramatically reduced ocean traffic and the company slowly dwindled in size, laying up ships or scrapping them to save the costs of operating them.

[8] By 1937, the United States Maritime Commission, a successor to the USSB, had taken over the remaining ships of the troubled line when it declared bankruptcy in 1937.