During World War I, as both SS Pennsylvanian and USS Scranton, the ship carried cargo and animals to France, and returned American troops after the Armistice in 1918.

This loss of access, coupled with the fact that the Panama Canal was not yet open, caused American-Hawaii to return in late April to its historic route of sailing around South America via the Straits of Magellan.

Assigned to the Navy's Naval Overseas Transportation Service (NOTS), Pennsylvanian loaded a general cargo and sailed for Brest, France, on 30 September.

While sailing to France to begin her first troop-carrying duties in late March, Scranton suffered damage to her rudder and was disabled 900 nautical miles (1,700 km) east of New York.

[21] During the day on 28 March,[23] Scranton attempted to run a towline to El Sol by sending a launch in the rolling seas, but it capsized, drowning three men.

[25] After repairs, Scranton made three roundtrips to France and carried some 6,000 troops and passengers home to the United States before she was decommissioned on 19 July.

Though the company had abandoned its original Hawaiian sugar routes by this time,[20] Pennsylvanian continued inter-coastal service through the Panama Canal in a relatively uneventful career.

In October 1929, the Los Angeles Times reported on a shipment that included 2,500 to 3,000 radio sets among Pennsylvanian's 2,300 long tons (2,340 t) of cargo.

[27] In March 1938, The Christian Science Monitor reported that Pennsylvanian's captain, C. M. Bamforth, had temporarily turned the deck of the cargo ship into a boatyard to build a 15-foot (4.6 m) catboat for his son in Swampscott, Massachusetts.

Bamforth laid the keel while in San Francisco, bought copper rivets for the hull planking in Portland, Oregon, and began painting the boat after Pennsylvanian had traversed the Panama Canal.

[28] In October the same year, Pennsylvanian delivered 325 long tons (330 t) of steel parts for the Hale Telescope then under construction at the Palomar Observatory outside San Diego.

[30] From July to September 1942, Pennsylvanian sailed between New York and Caribbean ports, calling at Trinidad, Key West, Hampton Roads, Guantánamo Bay, and Cristóbal.

[31] Between May and September 1943, Pennsylvanian made four transatlantic crossings between New York and Liverpool, making intermediate stops in Loch Ewe and Methil while in the United Kingdom.

The cargo ship made two New York – Guantánamo Bay roundtrips between September and December before resuming transatlantic sailings.