The Great Depression brought difficult times for the Dollar Steamship Line. On June 3, 1938, the Coolidge was held in San Francisco because of $35,000 in unpaid debt of. A bond of $70,000 was put up so the ship could be released for its trip to Asia, but the Dollar Steamship Line was suspended from operation. As a result of increasing debt and decreasing patronage due to the war in China, the ownership of the SS President Coolidge (as well as all the other Dollar vessels) passed officially to a new Government owned line-the American President Lines Ltd.-on November 1, 1938. Despite the change in ownership, the Coolidge continued its trans-pacific runs. In July 1939, just over two years after the Buck incident, the Coolidge was in trouble again when she collided with the Nissan Maru, a Japanese freighter, on the Whangpoo River in China. The Coolidge suffered only minor damage.

From October 1940 through most of 1941, the Coolidge was used to evacuate Americans from Hong Kong because of the increasing fear of Japanese invasion. On January 16, 1941, the Coolidge arrived in San Francisco with 832 passengers, most of who were refugees and evacuees. This was a new record for passengers carried on a merchant ship on a regular run. On May 30, 1941, she arrived in San Francisco with more than 1,000 passengers-again, mostly refugees and evacuees. Japanese military presence in Asian waters was increasing and on her next trip in June 1941, the Coolidge encountered more than 100 Japanese war and supply ships in the Formosa Strait.

With the war in Europe and in the Asia/Pacific region getting worse, President Franklin D. Roosevelt declared a state of national emergency on May 28, 1941. Four days later, on June 2, 1941, the Coolidge was taken over by the Maritime Commission as a troop transport for the Army and, on July 15, 1941, left San Francisco on a voyage to Honolulu and the Philippines carrying troops. On the return trip, the Coolidge was refused permission to enter Japan to collect 100 Americans from Yokohama. She returned to San Francisco from Manila with 250 Americans. During the stopover in Hong Kong, Quan Wei and his family boarded the Coolidge en route to the US. The evacuees from Manila, Hong Kong, and Shanghai, including the Quan family, arrived in San Francisco on August 28, 1941.

The Coolidge left San Francisco on September 8, 1941 for Asia and was escorted for part of the Honolulu to Manila section by a cruiser and several patrol boats. The ship again left San Francisco on November 1, 1941 for Honolulu and Manila. On December 7, 1941 (December 8 local time on the ship), when the Coolidge was halfway from Manila to Honolulu, being escorted by the heavy cruiser USS Louisville, the Japanese Imperial Navy attacked Pearl Harbor.

The ship arrived in Honolulu a little over a week after the surprise attack on Pearl Harbor. On December 19, 125 seamen injured during the attack were taken on board the Coolidge and set off for San Francisco in a convoy of ships. Under the threat of Japanese attack, particularly from rumored Japanese submarines, the Coolidge traveled a northern, indirect route without exterior lights and boarded up portholes to prevent light showing. The Coolidge arrived in San Francisco on Christmas Day morning, with 124 patients-less one man who died on Christmas Eve from bad burns.

By January 1942, the Coolidge was converted to a troopship, almost a month ahead of President Roosevelt's order that brought all US shipping under Government control. During the conversion, the Coolidge was modified with guns and the standard navy gray paint. With much of the fine furnishings removed and fixed features covered up, the ship was then able to carry over 5,000 soldiers. For the next nine months, the Coolidge completed six military missions ferrying troops and equipment across the Pacific to the war front, traveling between places such as Australia, New Zealand, French Polynesia, Fiji, and San Francisco. In March 1942, following President Roosevelt's direct order, General Douglas Macarthur left the Philippines, but not before proclaim his now-famous words, "I shall return." General Douglas Macarthur returned to the US on board the Coolidge in May.