She was assigned a homeport of Portland, Maine, after commissioning and cruised as far south as Cape Ann, Massachusetts, serving in a law enforcement and search and rescue capacity.

She continued to guard that area and patrol until 5 May, when she was ordered to report to the Portsmouth Naval Shipyard at Kittery, Maine, for refit of her guns.

Ossipee continued to serve with the Nantucket Detachment until orders were received to report to the Boston Navy Yard to be outfitted for overseas duty.

[5] Ossipee served as a danger zone escort from the time of her arrival at Gibraltar until 30 October, with the exception of three special service cruises of short duration.

Ossipee sounded "general quarters," and in an attempt to drop depth charges on the unseen enemy, the cutter made full speed and the helm was cut hard to port.

"Secure" was sounded at 10:20 a.m., and Ossipee and the danger zone escort vessels that had been searching for the enemy U-boat proceeded at full speed to rejoin the convoy.

The cutter proceeded at full speed to the place where the submarine had disappeared and dropped two depth charges as close to the spot as could be ascertained in the darkness, but with no apparent result.

After being drydocked at the base, Ossipee, on 26 April, resumed her voyages from Gibraltar to British waters and returned as the ocean escort for different convoys bound in those directions.

The cutter proceeded to steam for the enemy's wake and dropped seven depth mines as nearly as could be ascertained around the spot where it had disappeared and zigzagged at full speed all around its supposed position, but apparently without result.

On 1 May, the danger zone escort joined up with the convoy and on 3 May, Ossipee proceeded to Pembroke Dock, Wales, where she arrived the same day.

Continuing on her voyage the danger zone escort from Gibraltar joined the fleet on 21 May, and all of the ships arrived safely at the base on 23 May.

The general alarm was sounded and all hands being at quarters, Ossipee proceeded at full speed to the vicinity of the spot where it was supposed that the submarine had fired the torpedo.

Captain Wheeler, in his official report stated that, while there was little doubt that City of Oxford did see the torpedo, it appeared that it had been fired at long range, making it very difficult to locate the enemy.

Ossipee and Seneca proceeded to Pembroke Dock, Wales, in company where they arrived later the same day, having anchored in Dale Roads on 21 October.

All hands were called to quarters and under full speed, the cutter proceeded to the vicinity where the flash was seen and dropped two depth charges near the spot.

No evidence of a submarine was found, but it was always deemed necessary and good policy to drop one or more depth charges for the purpose of reminding the enemy that his presence was known, even if his position was not.

Releasing these two canisters at 5:35 p.m. and seeing nothing of the enemy, "secure" was sounded and Ossipee rejoined the convoy, which proceeded to its rendezvous with the Gibraltar Danger Zone Escort on 31 October.

Ossipee remained until 8 November, when she left on a return voyage to British waters with the last convoy with which she was to be associated with during the period of hostilities.

On the day of the Armistice, 11 November, at noon, Ossipee, with her convoy at 39°51'N, 11°50'W, turned on the regular navigation lights indicating that news had been received of the cessation of hostilities.

[1] On 17 November 1924 Ossipee rescued the crew of barge Canesto that was sinking in the Atlantic Ocean between New York City and Rockland, Maine, when the tug Kingfisher's steering failed in a gale.

[6] On 27 December 1925, Ossipee was among the vessels responding to a fire aboard the Edward J. Lawrence moored in Portland Harbor,[7] at the time the last remaining six-masted schooner afloat.

Efforts to extinguish the blaze were unsuccessful as thousands of people looked on, with the Edward J. Lawrence ultimately maneuvered aground in shallow waters nearby and allowed to burn and sink.

On 22 October 1943, the U.S. Army Corps of Engineers derrick barge Tonowanda and two dump scows went ashore east of Cleveland harbor during a storm, and Ossipee was dispatched to stand by and assist.

Early in June 1945, she conducted drills and exercises in Lake Erie, later in the month towing U.S. Navy YF-737 to Chicago, and returning to Cleveland.