D-Day was the largest invasion ever assembled, before or since, landed 156,000 Allied troops by sea and air on five beachheads in Normandy, France. The USS Laffey participated in screening and bombardment for Utah Beach, the most western beach between Pouppeville and La Madeleine.

Operation Neptune was the codename for the operation carried out by allied naval forces to support the efforts at Normandy on D-Day. The allied naval forces were asked to convey the ground forces to the area for assault on a hostile and defended shore, assist their landings by gunfire support, protect their lines of communication against enemy surface and underwater attack, and insure the flow of supplies for an indefinite period of future operations. There were 6,939 vessels that participated in Operation Neptune and the D-Day invasions. Of these vessels, 80% were British and 16.5% American ships.

There were 34 U.S. destroyers and destroyer escorts that helped support the efforts at Normandy, including the USS Laffey DD-724. The Navy's small destroyers took position on the front line of this fire support. With their shallow draft, they were able to come closer to shore than the heavier battleships and cruisers which allowed them to provide direct gunfire support for troops on the beach.

The USS Laffey was commissioned in February 1944 and after months of training, she arrived in England on 27 May to support the efforts in Normandy for D-Day as part of Operation Neptune. On 3 June she headed for the Normandy beaches escorting tugs, landing craft, and two Dutch gunboats. The group arrived in the assault area, off Utah Beach, Baie de la Siene, France, at dawn on D-Day, 6 June. On the 6th and 7th, Laffey screened to seaward; and on the 8th and 9th, she bombarded gun emplacements with good results. Leaving the screen temporarily, the ship raced to Plymouth, England to replenish and returned to the coast of Normandy the next day. On 12 June Laffey pursued enemy "E" boats which had torpedoed destroyer Nelson. The destroyer broke up their tight formation and prevented further attacks.

Screening duties completed, the ship returned to England, arriving at Portsmouth 22 June where she tied up alongside Nevada. On 25 June she got underway with the battleship to join Bombardment Group 2 shelling the formidable defenses at Cherbourg, France. Upon reaching the bombardment area, the group was taken under fire by shore batteries; and destroyers Bartonand O’Brien were hit. Laffey was hit above the waterline by a richocheting shell that failed to explode and did little damage.

Late that day the bombardment group retired and headed for England, arriving at Belfast 1 July 1944. She sailed with Destroyer Division 119 three days later for home, arriving at Boston 9 July.

All total, 73,000 American troops landed at Normandy during the D-Day Invasion. At least 200 ships and landing craft, including three U.S. destroyers, were sunk while defending the troops and providing support at D-Day. At Utah Beach, where the USS Laffey provided support, casualties were the lightest of all landings – out of 23,000 troops, only 197 men were killed or wounded. D-Day was the start of Allied operations which would ultimately liberate Western Europe, defeat Nazi Germany and end the Second World War.

While D-Day began on 6 June 1944, the operations continued until 30 June 1944 when allied forces had taken full control at Normandy.