Still outfitting when the United States entered World War II, Ellyson was quickly readied for sea and patrolled in the Atlantic, protecting Allied shipping from Halifax, Nova Scotia, to the West Indies and Panama Canal. On 14 January 1942 she rescued 24 survivors from the sunken Norwegian SS Norness. On 15 June she broke the pennant of Commander, Destroyer Squadron 10, which she was to carry proudly through the war, through the squadron's redesignation to Mine Division 20 and the subsequent conversion of its destroyers to high-speed minesweepers.
In August 1942 Ellyson began operating with the aircraft carrierRanger, and remained with her through the landings at Fedhala, French Morocco, on 8 November. After two months of escort duty along the east coast, she rejoined Ranger on two voyages to Casablanca to ferry Army planes to north Africa.
On 6 January 1944 Ellyson once again joined Ranger for screen and plane guard duty in Narragansett Bay. She sailed for north Africa 19 April and arrived at Oran on 1 May. On the 16th while hunting submarinesEllyson made contact on U-616, touching off an intensive coordinated air-sea hunt. The submarine surfaced at 23:58, and soon dived after a brief duel with Macomb. Ellyson and Hambleton continued the attack with depth charges, forcing U-616 to surface again. Ellyson sank her with gunfire on the morning of the 17th, then rescued 30 survivors.
Ellyson arrived at Plymouth, on 22 May 1944 for last-minute preparations for the invasion of France. On 6 June she covered the Army Ranger assault on Pointe du Hoc to knock out the heavy gun emplacements reported there. On 25 June she saw action off Cherbourg, blasting gun installations, destroying naval mines, and laying a smoke screen for larger fleet units.
Ellyson sailed from Portland Harbour on 29 June 1944, to invade southern France on 15 August. She led the destroyer fires support group in directly behind the minesweepers and knocked out defenses for the incoming troops. On patrol on 27 August she illuminated a suspicious fishing vessel and captured it, finding 50 German submariners trying to escape. Ellyson remained on patrol to cover the landing of reinforcements and support the invasion until October, then sailed for Boston, arriving 8 November to begin conversion to a high-speed minesweeper. She was reclassified to hull classification symbolDMS-19 on 15 November 1944.
1945
After training in Chesapeake Bay, Ellyson sailed from Norfolk, on 3 January 1945 for the Pacific. On 24 March she arrived off Okinawa with the rest of her squadron to sweep in advance of the invasion. After thus making possible the pre-assault bombardment, she supported smaller minesweepers clearing approaches to the beaches and inner harbors. After the landings of 1 April Ellyson joined the radar picket line. The varied and dangerous duties assigned her squadron in the Okinawa operation took a heavy toll, only three of the 12 ships with whom she sailed in the next three months survived undamaged. Ellyson went to the aid of her sister shipEmmons on 6 April, attempting to tow the abandoned kamikaze victim. Flames and the threat of a magazine explosion forced Ellyson to sink the stricken destroyer early on 7 April to prevent her drifting on to Japanese-held Ie Shima. Ellyson herself was attacked several times and accounted for a number of Japanese planes.
In July 1945 Ellyson became flagship for the task group sweeping the East China Sea. Upon the ceasefire, she joined Third Fleet off Tokyo Bay and cleared it for the incoming occupation fleet units. In September she returned to Okinawa, and from her base at Buckner Bay, served as command ship for clearing the Inland Sea. She sailed from Japan on 5 December for Norfolk, arriving 5 January 1946.
Post war
Ellyson remained in the Atlantic, based at Charleston, South Carolina, primarily, for training as far as the Caribbean Sea. In 1948 she was immobilized at Charleston, resumed operations that November when she sailed to Argentia to sweep for an amphibious exercise. Attached to Mine Force, Atlantic Fleet, Ellyson continued to operate from Charleston on training duty along the east coast and in the Caribbean. She served in the Mediterranean with the Sixth Fleet in 1949, 1951, and 1953. On 4 May 1954 her hull classification symbol reverted to DD-454.