Equipped with specialized meteorological instruments,
Manhasset joined the weather patrol in the North Atlantic Ocean to gather vital weather information used in compiling forecasts for Allied European operations against the
Axis. She braved the dangers of stormy seas and the menace of German
U-boats while operating her assigned and isolated patrol areas out of
Argentia, Newfoundland, and
Boston, Massachusetts. She averaged about one patrol a month, usually about three weeks long.
Manhasset also patrolled and searched for German submarines. While cruising midway between
Flemish Cap and
Cape Farewell, Greenland, she
depth charged a suspected U-boat, with no positive results, 27 April 1943. The following week convoy ONS 5 (
Outbound from Liverpool to
Nova Scotia,
Slow) steamed through her patrol station, and on 5 May she provided support during one of the largest convoy battles of World War II, the convoy included 43 merchant vessels, 7 escorts, 2 trawlers, and a fuel ship and was joined by other Allied ships as the battle progressed. Attacking them were members of three
Wolfpacks,
Specht, Meisel, and Amsel, including 58 U-boats. The battle raged between late 4 May and early 6 May. Although the convoy lost 13 ships, the escorts sank five U-boats and repulsed the remainder. Occurring in "
Black May," the month marking the dramatic decline in the U-boat effectiveness in WWII, when Allied efforts repulsed or sank most opposition, the Battle with ONS 5 was the final wolfpack attack against the northern merchant trade routes in the Battle of the North Atlantic. As
Manhasset patrolled near the British merchant ship
Dolius,
torpedoed and abandoned earlier in the day but still afloat, she made sound contact with a submarine late in the afternoon. She made six vigorous depth charge attacks and sighted first a
periscope wake followed by an oil slick. However, she sighted no wreckage and broke off attack to guard the torpedoed ship after more than 2 hours of searching.
Transferred to the Coast Guard Manhasset contained her weather station patrols during the rest of the war. The Navy transferred her to the
U.S. Coast Guard 22 October 1943, and her name was struck from the
Navy List 30 October 1943. ==Post-war dispositioning ==