Legare continued to operate from Norfolk after the United States entered World War II with the Japanese attack on Pearl Harbor on 7 December 1941.

While on patrol on 19 March 1942, she received word of a submarine contact 8 nautical miles (15 km; 9.2 mi) south of Hatteras, North Carolina.

Her crew observed Oil, debris, and air bubbles on the surface, but the sinking of a submarine at that position on that date was not confirmed by captured documents examined after the war.

On 14 April 1942, Legare was about 100 nautical miles (185 km; 115 mi) off Cape Charles, Virginia, when she detected a submarine on the surface at 20:30 and closed to investigate.

[1] Legare exchanged recognition with the submarine and established that she was a United States Navy vessel, USS Mackerel (SS-204), making a voyage on the surface from New London, Connecticut, to Norfolk.

[3] A subsequent investigation of the incident by the Eastern Sea Frontier found it impossible to reconcile the reports of the two vessels and concluded that Mackerel had mistakenly fired a torpedo at Legare.

Stockholm's special bow, designed to cut through ice, struck Andrea Doria amidships, ripping a great hole her side.

During the early-morning hours of 26 July 1956, Legare departed her home port of New Bedford, the first U.S. Coast Guard cutter to respond to an SOS from Andrea Doria.

One of many ships to respond, Legare was the first U.S. Coast Guard cutter to arrive at the scene of the disaster and was present for the entire rescue operation.

She rescued survivors from Andrea Doria's lifeboats and transported them to larger vessels on the scene, such as the French Line's SS Île de France, which had diverted from her eastbound voyage from New York City to her home port of Le Havre, France, to render assistance to Andrea Doria.