Panama Pacific Line was established as a subsidiary of International Mercantile Marine (IMM) to transport passengers and cargo via the Panama Canal between the East and West Coasts of the United States.

Even though IMM had started making plans for this intercoastal service in 1911, service only started in May 1915 with the ships Kroonland and Finland, which were from another subsidiary line of IMM. Kroonland and Finland were transferred to the IMM's American Line following the prolonged closure of the canal as a result of landslides in September 1915. The intercoastal service was halted as a result of the outbreak of World War I and the strain it placed on international shipping.

Manchuria at the New Municipal Pier in San Diego, California, in 1925. As a result of increased demand, San Diego became a port of call for the Panama Pacific.
Along with the American Line passenger steamer Manchuria, Kroonland and Finland were reinstated on the restored intercoastal route in 1923. In 1925, Mongolia, the sister ship of Manchuria, overtook Kroonland on the route.

California, Virginia, and Pennsylvania—three ships with steam turbo generators and turbo-electric transmission—were put into service in 1928–1929 to take the place of all other intercoastal service vessels. These three most recent ships had a drive-on service for passengers' automobiles. This made it possible for passengers to disembark with their automobiles at ports of call like Havana, which was added at the beginning of the 1930s.