By May 1944, 1.5 million American troops had arrived in the United Kingdom. Most were housed in temporary camps in the south-west of England, ready to move across the Channel to the western section of the landing zone. British and Canadian troops were billeted in accommodation further east, spread from Southampton to Newhaven, and even on the east coast for men who would be coming across in later waves. A complex system called Movement Control assured that the men and vehicles left on schedule from twenty departure points. Some men had to board their craft nearly a week before departure. The ships met at a rendezvous point (nicknamed "Piccadilly Circus") south-east of the Isle of Wight to assemble into convoys to cross the Channel. Minesweepers began clearing lanes on the evening of 5 June, and a thousand bombers left before dawn to attack the coastal defences. Some 1,200 aircraft departed England just before midnight to transport three airborne divisions to their drop zones behind enemy lines several hours before the beach landings.
The American 82nd and 101st Airborne Divisions were assigned objectives on the Cotentin Peninsula west of Utah. The British 6th Airborne Division was assigned to capture intact the bridges over the Caen Canal and River Orne. The Free French 4th SAS battalion of 538 men was assigned objectives in Brittany (Operation Dingson, Operation Samwest). The airborne landings west of Utah were not very successful, as only ten per cent of the paratroopers landed in their drop zones. Gathering the men together into fighting units was made difficult by a shortage of radios and by the terrain, with its hedgerows, stone walls and marshes. The 82nd Airborne Division captured its primary objective at Sainte-Mère-Église and worked to protect the western flank. Its failure to capture the river crossings at the River Merderet resulted in a delay in sealing off the Cotentin Peninsula. The 101st Airborne Division helped protect the southern flank and captured the lock on the River Douve at La Barquette, but did not capture the assigned nearby bridges on the first day.
Some 132,000 men were transported by sea on D-Day, and a further 24,000 came by air. Preliminary naval bombardment commenced at 05:45 and continued until 06:25 from five battleships, twenty cruisers, sixty-five destroyers, and two monitors. Infantry began arriving on the beaches at around 06:30.
The craft bearing the U.S. 4th Infantry Division assaulting Utah were pushed by the current to a spot about 1,800 metres (2,000 yd) south of their intended landing zone. The troops met light resistance, suffering fewer than 200 casualties. Their efforts to push inland fell far short of their targets for the first day, but they were able to advance about 4 miles (6.4 km), making contact with the 101st Airborne Division. At Pointe du Hoc, the task for the two hundred men of the 2nd Ranger Battalion, commanded by Lieutenant Colonel James Rudder, was to scale the 30 metres (98 ft) cliffs with ropes and ladders to destroy the gun battery located there. While under fire from above, the men scaled the cliff, only to discover that the guns had already been withdrawn. The Rangers located the weapons, unguarded but ready to use, in an orchard some 550 metres (600 yd) south of the point, and disabled them. Under attack, the men at the point became isolated, and some were captured. By dawn on D+1, Rudder had only 90 men able to fight. Relief did not come until D+2, when members of the 743rd Tank Battalion arrived.
At Gold, high winds made conditions difficult for the landing craft, and the amphibious DD tanks were landed close to shore or directly on the beach instead of further out as planned. Aerial attacks had failed to hit the Le Hamel strong point, and its 75 mm gun continued to do damage until 16:00. On the western flank, the 1st Battalion, Hampshire Regiment captured Arromanches (future site of Mulberry "B"), and contact was made on the eastern flank with the Canadian forces at Juno. The ruins of Mulberry Harbour B are still visible in the town of Arromanches to this day.
Landings of infantry at Juno were delayed because of rough seas, and the men arrived ahead of their supporting armour, suffering many casualties while disembarking. Most of the offshore bombardment had missed the German defences. In spite of these difficulties, the Canadians quickly cleared the beach and created two exits to the villages above. Delays in taking Bény-sur-Mer led to congestion on the beach, but by nightfall the contiguous Juno and Gold beachheads covered an area 12 miles (19 km) wide and 7 miles (10 km) deep. Casualties at Juno were 961 men.
On Sword, 21 of 25 DD tanks succeeded in getting safely ashore to provide cover for the infantry, who began disembarking at 07:30. They quickly cleared the beach and created several exits for the tanks. In the windy conditions, the tide came in more quickly than expected, making manoeuvring the armour difficult. The 2nd Battalion, King's Shropshire Light Infantry advanced on foot to within a few kilometres of Caen, but had to withdraw due to lack of armour support. At 16:00, the German 21st Panzer Division mounted a counterattack between Sword and Juno and nearly succeeded in reaching the coast. They met stiff resistance from the British 3rd Infantry Division and were soon recalled to assist in the area between Caen and Bayeux.
Omaha, the most heavily defended sector, was assigned to the U.S. 1st Infantry Division, supplemented by troops from the U.S. 29th Infantry Division. They faced the 352nd Infantry Division, rather than the expected single regiment. Strong currents forced many landing craft east of their intended position or delayed them. Casualties were heavier than all the other landings combined, as the men were subjected to fire from the cliffs above. Problems clearing the beach of obstructions led to the beachmaster calling a halt to further landings of vehicles at 08:30. A group of destroyers arrived around this time to offer supporting artillery fire. Exit from Omaha was possible only via five gullies, and by late morning barely six hundred men had reached the higher ground. By noon, as the artillery fire took its toll and the Germans started to run out of ammunition, the Americans were able to clear some lanes on the beaches. They also started clearing the draws of enemy defences so that vehicles could move off the beach. The tenuous beachhead was expanded over the following days, and the D-Day objectives were accomplished by D+3.
The first components of the Mulberry harbours were brought across on D+1 and the structures were in use for unloading by mid-June. One was constructed at Arromanches by the British, the other at Omaha by the Americans. Severe storms on 19 June interrupted the landing of supplies and destroyed the Omaha harbour. The repaired Arromanches harbour was able to receive around 6,000 tons of materiel daily and was in continuous use for the next ten months, but most shipments were brought in over the beaches until the port of Cherbourg was cleared of mines and obstructions on 16 July.
Allied casualties on the first day were at least 10,000, with 4,414 confirmed dead. The Germans lost 1,000 men. The Allied invasion plans had called for the capture of Carentan, St. Lô, Caen, and Bayeux on the first day, with all the beaches (other than Utah), linked with a front line 10 to 16 kilometres (6 to 10 mi) from the beaches; none of these objectives were achieved. The five beachheads were not connected until 12 June, by which time the Allies held a front around 97 kilometres (60 mi) long and 24 kilometres (15 mi) deep. Caen, a major objective, was still in German hands at the end of D-Day and would not be completely captured until 21 July. Nearly 160,000 troops crossed the English Channel on 6 June, and more than two million Allied troops were in France by the end of August.