The sector which was attacked was guarded by four divisions, of which the 352nd and 91st were of high quality. The other defending troops included Germans who were not fit for active duty on the Eastern Front, conscripted Poles and former Soviet prisoners-of-war who had agreed to fight for the Germans. These units had German leaders.
Rommel's defensive measures were made difficult by arguments over how to use armoured forces. Von Geyr and Rommel disagreed over the how to use Panzer divisions.
Rommel thought armoured formations be close to the coast, to attack while the invaders were weak. Von Geyr said they should instead be put around Paris and used in a big group when the Germans knew which beach was being invaded. Hitler made a compromise solution.
Rommel was given only three tank divisions, one of which was close enough to the Normandy beaches to fight on the first day. The other mechanized divisions were put under the control of the German Armed Forces HQ (OKW) and were placed across France, Belgium and the Netherlands.
The opportunity for launching an invasion was limited to only a few days in each month, because a full moon was needed. This would provide light for the aircraft pilots and create a spring tide. Eisenhower had picked 5 June as the date for the assault. However, on 4 June, conditions were unsuitable for a landing. High winds and heavy seas made it impossible to launch landing craft. Low clouds would prevent aircraft finding their targets.
Meteorologists predicted an improvement in the weather for 6 June. At a meeting on 5 June, Eisenhower and his senior commanders discussed the situation. Eisenhower decided to launch the invasion that night. Had Eisenhower delayed the invasion, the only option was to go two weeks later. This would have been during stormy weather.
To make it hard for the Germans to launch attacks during the sea attack phase, airborne operations were used to capture bridges and road crossings. The airborne landings behind the beaches were also designed to help the soldiers landing on beaches and destroy German coastal defense artillery.
On Sword Beach, the regular British infantry came ashore with few casualties. They had advanced about by the end of the day but did not get as far as Montgomery had wanted. Caen was still held by Germans by the end of D-Day and would remain so until Operation Charnwood on 9 July.
The Canadian forces that landed on Juno Beach had a difficult battle. German concrete fortifications and a sea wall twice as high as at Omaha Beach made it very difficult to attack. Juno was the second most heavily defended beach on D-Day, next to Omaha. Canadians were off the beach within hours and advancing inland. They were the only units to reach their D-Day goals, although most units fell back a few kilometres to make stronger defensive positions.
At Gold Beach, there were many dead and wounded because the Germans had strongly fortified a village on the beach. The 50th (Northumbrian) Infantry Division advanced almost to Bayeux by the end of the day. When commando units captured the Port-en-Bessin, the Allies could use their PLUTO pipeline to bring in fuel.
The Americans who landed on Omaha Beach faced the veteran German 352nd Infantry Division, one of the best trained groups on the beaches. Furthermore, Omaha was the most heavily fortified beach. Commanders considered abandoning the beach but small units of infantry got past the coastal defences. By the end of day two areas had been captured. The control over the beach expanded over the following days and the D-Day goals were accomplished by D+3.
At Pointe du Hoc, the 2nd Ranger battalion had to climb the cliffs. While they climbed, the enemy shot at them and dropped grenades. They used ropes and ladders to climb up and then destroy the guns.
The beach fortifications were important targets since a single artillery observer could have directed fire on the U.S. beaches. The Rangers captured the fortifications. They then had to fight for 2 days to hold the location, losing more than 60 percent of their men.
The number of dead and wounded on Utah Beach, the westernmost landing zone, were the lightest of any beach. Only 197 out of the 23,000 troops that landed were killed or wounded. The 4th Infantry Division troops that landed on the beach was able to move inland by early afternoon, linking up with the 101st Airborne Division.
Once the beaches were controlled, the Mulberry Harbours were set up around 9 June. One was constructed at Arromanches by British forces, the other at Omaha Beach by American forces. Severe storms on 19 June caused problems with the landing of supplies and destroyed the Omaha harbour. The Arromanches harbour was able to supply around 9,000 tons daily until the end of August 1944, by which time the port of Cherbourg had been captured by the Allies.
The German 21st Panzer division attacked between Sword and Juno beaches and nearly reached the Channel. Allied anti-tank gunners made them pull back before the end of 6 June.
The Allied invasion plans had called for the capture of Carentan, St. Lô, Caen and Bayeux on the first day. The plan was to link all the beaches except Utah and Sword (the last linked with paratroopers) and a front line from the beaches. None of these goals had been achieved. The number of dead and wounded had not been as heavy as some had feared (around 10,000 compared to the 20,000 Churchill had estimated) and the bridges had survived the German attacks.
In the western part of the invasion area, US troops were to occupy the Cotentin Peninsula, especially Cherbourg. This would provide the Allies with a deep water harbour. The land behind Utah and Omaha was banks and hedgerows that tanks, gunfire and vision could not get through. This made them ideal defensive positions.
The U.S. infantry made slow progress and had many dead and wounded as they moved towards Cherbourg. The airborne troops were used to help with the advance. The far side of the peninsula was reached on 18 June. Hitler told German forces not to retreat to the strong Atlantic Wall fortifications in Cherbourg. The Cherbourg commander, Lieutenant General von Schlieben, surrendered on 26 June. Before surrendering he had most of the facilities destroyed, making the harbour inoperable until the middle of August, by which time the combat front had moved so far east that it was less helpful.
While the Americans headed for Cherbourg, a unit of troops led by the British moved towards Caen. Montgomery made many attrition warfare attacks. The first was Operation Perch, which moved south from Bayeux to Villers-Bocage where the armour could capture Caen. It was halted at the Battle of Villers-Bocage. Caen was bombed and then occupied north of the River Orne in Operation Charnwood from 7 July until 9 July. An attack in the Caen area followed with all three British armoured divisions, codenamed "Operation Goodwood" from 18 July until 21 July. It captured the high ground south of Caen. The rest of the city was captured by Canadian forces during Operation Atlantic. A further operation, Operation Spring, from 25 July until 28 July, by the Canadians secured limited land south of the city, but with many dead and wounded.
Montgomery's plan included keeping the Germans in the eastern part of the invasion area, while protecting Cobra's position. By the end of Goodwood, the Germans had used the last of their reserve divisions; there were six and a half Panzer divisions against the British and Canadian forces compared to one and a half facing the United States armies.
"Operation Cobra" was launched on 25 July by the U.S. First Army. It was successful. The VIII Corps entered Coutances at the western end of the Cotentin Peninsula on 28 July, after breaking through the German lines.