Prefabricated harbours built on a huge scale never previously attempted played a vital role in the D-Day landings of 1944...

IT WAS one of the most daring of D-Day plans and one that was carried out in the utmost secrecy in the heart of Southampton and the surrounding area.

With the choice of Normandy as the invasion point came demands forced on the Allies by the natural geography of the beaches and the total lack of large harbours other than in the nearby fortresses of Le Havre and Cherbourg.

The solution was simply audacious - if the Allies could not capture a port then they must take one with them. It was from this germ of an idea that the project codenamed, Mulberry Harbour, took root.

Attended by Roosevelt and Churchill, the Quebec Conference of 1943 agreed to the idea for two such harbours, one each for the British and Americans.

Churchill's orders were characteristically blunt and to the point when he asked for piers which "must float up and down with the tide, the anchoring problem must be mastered. Let me have the best solution worked out. Don't argue the matter. The difficulties will argue for themselves.''

The whole project was of daunting dimensions - by May 1, 1944 harbours the size of Dover and exceeding, in area, the entire Southampton dock system had to be built.

Three weeks after the initial invasion forces had landed on the Normandy coast the Mulberries would have to be capable of dealing with anything up to 12,000 tons of stores and 2,500 vehicles a day.

On top of these requirements they had to be strong enough to weather the storms of the Channel and the dramatic tide differences of the Normandy coast. The docking facilities must be big enough to cope with the 26 foot draught of Liberty ships and at the same time provide sheltered water for smaller vessels, such as landing craft, to operate.

On completion all the components had to be towed nearly 100 miles across the Channel and assembled under the likelihood of strong enemy fire.

Most crucial to this imaginative plan was the fact that the whole operation had to be undertaken in total secrecy from beginning to end.

As one report was later to say: "Although sites as far apart as Southampton and Leith, North Wales and Oban were used, no one gave the secret away.''

The final design of the Mulberry Harbours called for a breakwater created by sunken ship hulks and the manufacture of an outer sea wall of huge concrete boxes which were given the codename, Phoenix.

These were enormous, the largest weighed more than 6,000 tons and was 60 feet tall. Many were built in the dry docks at Southampton and Portsmouth while smaller ones were constructed at Stokes Bay, Gosport and Beaulieu.

More than 20 different types were made, using more than one million tons of concrete and 70,000 tons of steel and at one point almost every creek, inlet and harbour in the south was being used as storage for parts of the Mulberry Harbour.

To confuse German intelligence and to speed up construction, the undertaking was carried out by scores of companies where something like 20,000 workers, in 12-hour shifts, toiled around the clock. Later the workforce was increased, some estimates putting the final figure at about 45,000.

Each building company was only given the barest details about what it had been asked to construct and no one, except for those at the highest level of command, knew the overall picture. A few weeks before June 6, planners decided to concentrate certain parts of the work around the Solent. Hundreds of skilled workers from all over the country poured into Southampton along with mountains of equipment which were quickly installed while work continued day and night.

Seven days before the invasion date the blockships, loaded with explosives, which were set to be scuttled as the outer parts of the Mulberries, sailed from Scotland on their one-way voyage to Normandy.

Two days before D-Day, Mulberry A and Mulberry B were ready. As they crossed the Channel they were described as "some weird procession of prehistoric monsters, these huge structures were towed across by 150 tugs, the biggest towing job in history.''

The assembly of the Mulberries began on D-Day plus one, the first convoy arriving in the assault area at 12.30pm. On the night of June 19 the biggest fear of the Mulberry Harbour planners became a cruel reality - a Channel gale started to blow, turning into the worst storm in living memory.

For three days the storm lashed the beaches and the troops causing havoc, while 500 landing craft rode out the storm inside the Arromanches Mulberry B Harbour.

The port was damaged, parts were lost while the piers and floating roadways took the brunt of the weather.

However it was the Americans who were hit worst of all. The gale ripped through the harbour off St Laurent, on Omaha Beach. The effect was devastating, and the place was wrecked. The storm literally overwhelmed the structure, blockships broke up, more than two-thirds of the harbour was lost.

The Allied build-up was seriously disrupted by the damage to the Mulberry installations but gradually the one-off Arromanches was brought back into commission.

By the end of June, 875,000 troops had been landed on the Normandy beaches as well as thousands of tons of stores and vehicles and much of this could not have taken place without the Mulberry Harbours.

Originally designed to have a life of just a few months, parts of these amazing structures can still be seen today resting on the gently shelving beach at Arromanches, the remaining hulks standing as monuments to a massive wartime effort.