D-Day: Mulberry harbours impressive, but doubts over their value: Huge prefabricated ports were towed across the Channel to provide safe havens. Will Bennett reports

The remains of the Mulberry Harbour in Arromanches can still be seen, while a section of the one at Omaha beach has been incorporated into a fishing jetty. They remain impressive monuments to the invasion of Normandy.

The two prefabricated harbours towed across the Channel by the Allies each covered two square miles, the size of the port of Dover. They were intended to provide a safe haven for shipping but now there are doubts as to their usefulness.

Their creation stemmed from the disastrous raid on Dieppe in 1942 after which it was realised that no major port was going to be captured either early or intact during an invasion.

The British-designed Mulberries, a code name selected at random, had an outer floating breakwater sheltering an inner fixed one built of huge hollow concrete boxes five stories high.

The first components were towed across the Channel the day after D-Day and submerged. Landing ships and small cargo vessels could unload directly while larger vessels could transfer their cargoes on to barges. The Allied landing areas were also protected by lines of scuttled blockships.

Less than a fortnight after D- Day the Mulberries were both in use - for the British at Arromanches and for the Americans at Omaha - and the final roadways were being brought across. But a huge storm destroyed these and by the third day the American harbour began to break up.

The remains of the latter were used to repair the British Mulberry and the Americans had to bring their supplies across the beaches. By the middle of July 35,000 tons a day were coming by this route which was more than when they had the Mulberry.

The British Mulberry stepped up its unloading to almost 7,000 tons a day but some historians doubt whether the artificial harbours justified their cost and the use of 45,000 men to build them.

The same applies to Pluto - Pipeline Under the Ocean. This was an impressive sounding piece of technology for supplying fuel to the Allied forces in Normandy which proved of limited use.

Pluto was a three-inch diameter steel pipe welded into sections more than 30 miles long and laid from huge drums across the Channel. In theory fuel could be landed at Liverpool and sent, via pumping stations in the Isle of Wight, direct to the armies in France.

In practice it could not be deployed until the port of Cherbourg had been captured and it then took time to lay. It went into operation on 18 September by which time the Allied armies were hundreds of miles away. Despite this, the Allied supply operation for the Normandy campaign remains one of the greatest logistical achievements in history.

In the first 24 days, 4,257 ships and other vessels arrived at the beachhead and by 25 July nearly 1.5 million troops had landed.

The Allied armies needed 26,000 tons of stores a day and, with absolute mastery of the air, only the storms disrupted the supply of reinforcements, vehicles, ammunition, fuel and food for the invaders.

(Photographs omitted)