It was more than a year after D-Day before one of the closest-kept of all Kingston's war secrets was revealed: that the Coronation Baths in Denmark Road had been used for training many of the frogmen who, on D-Day, carried out one of the most hazardous tasks of the war.

Clad in specially-designed rubber diving suits, they were the heroes who blasted a hole in the Nazis' Atlantic Wall and enabled the Allied invasion craft to reach the Normandy beaches.

During the spring of 1944, Kingstonians arrived at the baths to find the doors locked against them. They could not know that the reason they had been so annoyingly deprived of their swim was that the Admiralty was in occupation.

On these occasions, the main bath was filled with frogmen. They had to swim under water for prolonged periods, fixing objects to wooden structures representing enemy coastal defences, and practising cutting submarine nets.

Thanks to this training at Kingston and other centres, at H hour on D-Day 10 units, comprising some 120 officers and men, went into action and cleared a way through the enemy's underwater defences.

Slipping unobserved from small rubber dinghies, they swam beneath the surface to row upon row of massive underwater structures erected by the Germans. They cleared about 2,400 obstructions, most of them mined, and removed the charges from scores of Beetle tanks. Amazingly, only two of the frogmen were killed and 10 wounded.

After the war, journalists and cinema photographers came to Kingston from all over the UK to attend a demonstration by the secret D-Day swimmers. They were astonished to see that the frogmen had been trained to swim underwater in strict formation. They were even more astonished to see that, except for steering, the frogmen did not use their arms or hands for swimming. Their finned feet provided the propulsion.

The idea of rubber fins had been used by fishermen years before the war, but only in warm foreign water. Thus in 1943, when the Admiralty called in the Dunlop Rubber Company to assist in developing a diving suit that would completely enclose the diver, protect against the coldest water, and in which fins were an essential features, no samples of fins could be found anywhere in Britain.

That set a problem for Mr W G Gorham of Esher, loaned by Dunlop to the Admiralty for this special development work. Eventually, he got his main clues from a photograph of a film star, standing by a swimming pool wearing the type of fin needed.

Armed with this, and some sketchy descriptions, he produced the required results. The frogman's entire equipment weighed about 8lbs, and enabled him to remain under water for as long as 90 minues.

Underwater training would be difficult in Kingston today. The Coronation Baths closed in 1979 and were replaced, on a different site, by today's Kingfisher leisure pool, designed more for paddle-and-splash activities than swimming.

By the spring of 1944, two million tons of war materials, and more than 50,000 tanks and other military vehicles had been amassed in readiness for Operation Overlord, as D-Day was officially known.

Getting them across the Channel required strategy of the highest order. And having got them there, how were they to be off-loaded on a coastline that had no port?

The question was answered brilliantly with Mulberry Harbours, two huge artificial ports, each capable of taking ships weighing up to 10,000 tons. They were towed across the Channel in sections by a fleet of tugs. Within a few hours of the initial Overlord landings, the ports had been assembled, and men and supplies were being rushed ashore.

Plans for the harbours, without which the invasion could not have been accomplished, were devised by a brilliant engineer from Walton, Brig-adier Bruce White. After the war, his great achievement was rewarded with the KBE.

One of many local war secrets was that important components of the Mulberry Harbours were built by C H Coates of Chessington. It was one of the few firms that could provide the space and equipment for the construction of huge floats, built on the lines of snub-nosed submarines.

They were made from steel plate, and had to withstand a pressure of 8lbs to the square inch. These floats transported the great floating concrete caissons which formed the sea walls of the Mulberry Harbours.

Coates also provided "Hitler's coffins", so called because of their shape. They acted as an anchorage for the stanchions which, standing on the seabed, supported the harbours.

After a ferment of secret flurry, Coates managed to complete the floats and the "coffins" just a week before D-Day.

One of the harbours, built for the US beaches in Normandy, was smashed in a storm only two weeks after the invasion.

The other was for the British forces at Arromanches, and served its purpose gallantly. Within a week of installation, it had been used for the landing of 326 men, 100,000 tons of materials and some 54,000 tanks and vehicles.