Men and supplies were rushed into the beachheads as they were enlarged. Artificial harbours ('Mulberries') were quickly installed at 'Omaha' and 'Gold' beaches. But if the final outcome of the Allied invasion was to be a success, it was thought essential to capture the port of Cherbourg. Montgomery, who was in command, under Eisenhower, of all the ground troops, had heavy attacks made near Caen by British and Canadian troops. It was to pin down German strength there while the Americans broke out across the Cotentin peninsula. The Americans made a massive effort and captured the strongly fortified port. Unfortunately it had been wrecked by the Germans and could not be used for months. But, despite bad weather and the fact that the 'Omaha' Mulberry harbour had been smashed in a three-day storm, Allied supplies continued to pour in across the beaches and through the Mulberry at Arromanches.

The Americans then progressed southwards very slowly for three weeks. This, the 'Battle of the Hedgerows', was the worst phase of the campaign. The Germans fought skilfully in 'bocage' countryside, small fields enclosed by thick banks, hedgerows and deep-set roads. The Americans lost over 40 000 dead and wounded.

Montgomery, meanwhile, took Caen after a savage battle and then launched the huge attack with 750 tanks. But the formidable German Tiger tanks halted it, destroying over 200 tanks. Rommel had by then been badly injured in an air attack. Soon after, he committed suicide, which Hitler had invited him to do because of Rommel's connection with the July Plot to kill him.

The long-awaited break out from Normandy followed the Americans' victory at St Louis. They advanced with tanks and planes towards Avranches. General Patton, who had recently arrived in Normandy with another army (the 3rd) swept on into Brittany and then eastwards towards the River Seine. Hitler foolishly would not allow a German retreat from Normandy and ordered a powerful counter-attack towards Avranches. But the Ultra code- breakers gave four days notice of it and the attack was stopped by British and American air attacks.

At Le Mans, Patton turned one corps of troops northwards towards Calaise and formed the trap of the Calaise pocket, but to his annoyance was not allowed to close it. Roads in the pocket became choked with 3000 abandoned guns, tanks and vehicles and 60 000 Germans were captured or killed, although most of the panzers got away. The Allies pushed on towards the Seine and Paris was liberated.

Meanwhile, in the south of France, American and French troops had landed near Toulon and were advancing rapidly northwards to link with Patton's troops.

Germany's strength had collapsed in France after the battle of Normandy and Germany was wide open to invasion. The Allies did not exploit this chance. Montgomery wanted to make a powerful thrust into Germany past the north of the Siegfried Line, which he said would end the war in that year, 1944. Eisenhower would not let him do so. The Allies moved up to the Siegfried Line and halted. In the battle of Arnhem, Montgomery tried a bold and imaginative plan to cross the River Rhine at Arnhem in Holland. Two American airborne divisions were to take seven bridges in Holland while the British airborne division was to land at Arnhem and take the bridge there. But the British division was dropped a few kilometres north of Arnhem and two German panzer divisions, stationed nearby, attacked. The paratroopers held out against the attacks for nine days, but bad weather prevented reinforcements from getting through and the survivors were forced to retreat.