D-Day: Conditions helped Allies: Invasion went largely to plan but one battle threatened the entire operation. Christopher Bellamy looks at what went right and wrong

THE BRITISH Second Army under Lt- Gen Miles Dempsey landed on three beaches: Gold, Juno and Sword. Whereas the American beaches, Utah and Omaha, were widely separated, the British landing zones formed an almost continuous 25-mile stretch.

More importantly they were protected by the Calvados reef, which enabled the most of the amphibious DD (Duplex Drive) tanks to get ashore. Had Montgomery had his way and landed a day earlier in worse weather, the result could have been a disaster.

The first British troops landed on Sword at 7.25am and on Gold at 7.30am, while the Canadians attacked Juno at 7.45am. On all beaches, minesweeping flail tanks or 'crabs' and DD tanks led the way.

The plan was for landing craft to come close to the beach, each putting four swimming tanks ashore, followed five minutes later by the flail tanks to clear mines. Then came infantry in two waves followed by the beach command group and bulldozers to breach the sea wall.

Specialised armour followed next, then self-propelled artillery and finally stores and ammunition. It was a complicated plan and the successive groups became mixed up, piles of stranded equipment littering the shoreline.

Utah beach, on the east of the Cotentin peninsula, was the westernmost of the invasion beaches. The first US troops from the 4th Infantry Division landed at 6.30am. The current swept the Americans 2,000 yards south of their objective but the actual landing site proved better because it had carried them into the most lightly defended sector of the Normandy coast. Vehicles streamed in behind the assault troops who had found an undefended exit from the beach.

The Americans landed 23,000 men on Utah with only 197 casualties, an almost miraculous deliverance. Their real difficulties began once they started to push inland encountering swampy terrain and endless ditches.

Back in the British sector, 21,400 troops landed on Juno beach on D-Day, but only six of 40 landing craft with artillery on board arrived - the rest capsized. The infantry arrived ahead of the supporting DD tanks but the Canadians pressed on, avoiding pockets of German resistance and, as the plan demanded, pushed on inland.

Another 25,000 troops came ashore on Gold. By noon, tanks and self-propelled artillery had arrived and it was in full use as a reception area, except around Le Hamel, where British infantry battled until late afternoon. They could probably have taken Bayeux that night but were held back in case of a German counter-attack.

By 9am the British had overcome beach defences on Sword and had taken Hermanville-sur-Mer, a kilometre inland. By nightfall, the whole of the British Third Division was ashore with full tank support.

In the next few days, the division struggled to advance on Caen. The Germans halted them, and began to concentrate armour and reinforcements - the beginning of the 'hinge' around which the US forces would eventually swing.

(Maps omitted)