On D-Day, the untested 29th Infantry Division, joined by the veteran 1st Infantry Division and nine companies of U.S. Army Rangers redirected from Pointe du Hoc, were to assault the western half of the beach. The battle-hardened 1st Infantry Division was given the eastern half. The initial assault waves, consisting of tanks, infantry, and combat engineer forces, were carefully planned to reduce the coastal defenses and allow the larger ships of the follow-up waves to land.
The primary objective at Omaha was to secure a beachhead of some five miles (eight kilometres) depth, between Port-en-Bessin and the Vire River, linking with the British landings at Gold to the east, and reaching the area of Isigny to the west to link up with VII Corps landing at Utah.
Very little went as planned during the landing at Omaha. Difficulties in navigation caused the majority of landing craft to miss their targets throughout the day. The defenses were unexpectedly strong, and inflicted heavy casualties on landing US troops. Under heavy fire, the engineers struggled to clear the beach obstacles; later landings bunched up around the few channels that were cleared. Weakened by the casualties taken just in landing, the surviving assault troops could not clear the heavily defended exits off the beach. This caused further problems and consequent delays for later landings. Small penetrations were eventually achieved by groups of survivors making improvised assaults, scaling the bluffs between the most heavily defended points. By the end of the day, two small isolated footholds had been won, which were subsequently exploited against weaker defenses further inland, thus achieving the original D-Day objectives over the following days.
Once the beachhead had been secured, Omaha became the location of one of the two Mulberry harbours, prefabricated artificial harbours towed in pieces across the English Channel and assembled just off shore. Construction of 'Mulberry A' at Omaha began the day after D-Day with the scuttling of ships to form a breakwater. By D+10 the harbour became operational when the first pier was completed; LST 342 docking and unloading 78 vehicles in 38 minutes. Three days later the worst storm to hit Normandy in 40 years began to blow, raging for three days and not abating until the night of June 22. The harbour was so completely wrecked that the decision was taken not to repair it; supplies being subsequently landed directly on the beach until fixed port facilities were captured. In the few days that the harbour was operational, 11,000 troops, 2,000 vehicles and 9,000 tons of equipment and supplies were brought ashore. Over the 100 days following D-Day more than 1,000,000 tons of supplies, 100,000 vehicles and 600,000 men were landed, and 93,000 casualties were evacuated, via Omaha.
It is estimated that 3000 men were killed or wounded in taking the beach on D-Day although there are no exact figures available.