The construction was financed by Maryland Steel with a credit plan that called for a 5% down payment in cash, with nine monthly installments for the balance.

[7] She had a deadweight tonnage of 9,406 LT DWT, and her cargo holds, which had a storage capacity of 438,154 cu ft (12,407.1 m3),[2] were outfitted with a complete refrigeration plant so that she could carry perishable products from the West Coast—such as fresh produce from Southern California farms—to the East Coast.

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

Montanan had arrived in Los Angeles from Puget Sound on 22 January 1915 to complete her load before sailing for New York and Boston.

The almost fully loaded ship was slow to respond to the helm and ended up "ploughing through" 50 ft (15 m) of Municipal Pier A on Mormon Island channel before coming to a stop at a stone bulkhead.

The majority of the cargo was rice—from Japan, China, and California—which was destined for the United Kingdom to feed Indian troops fighting in Europe.

[18] In June, The Wall Street Journal reported that Montanan and Santa Clara (of the Grace Line) had sailed from Tacoma, Washington, with 2,500 tons of copper between them.

[19] In October 1915, landslides closed the Panama Canal and all American-Hawaiian ships, including Montanan, returned to the Straits of Magellan route again.

[25] The American convoy carrying the first units of the American Expeditionary Force was separated into four groups;[Note 5] Montanan was in the fourth group with her sister ship Dakotan, Army transports El Occidente and Edward Luckenbach, and escorts consisting of cruiser St. Louis, U.S. Navy transport Hancock, and destroyers Shaw, Ammen, and Flusser.

[30] Montanan departed Saint-Nazaire on 14 July in the company of her convoy mates El Occidente, Dakotan, and Edward Luckenbach.

[32][33] Escorted by armed yacht Noma, destroyers Burrows and Smith, and French cruiser Marseillaise,[33][34] the convoy was 500 nmi (600 mi; 900 km) west of its destination of Le Verdon-sur-Mer by the end of the day on 15 August.

Two of Montanan's Naval Armed Guardsmen drowned when their lifeboat capsized in the heavy seas;[35] three of her civilian crewmen also died in the attack.

[7][9] Shortly after Montanan was attacked, West Bridge, which had previously developed engine trouble and was drifting, was torpedoed by U-107 and abandoned.