In the spring of 1943 they had arrived in the Norfolk countryside in sinister convoys, villagers instructed to draw their curtains as the military low-loaders passed.

However, in bright sunshine at Fritton Lake, near Great Yarmouth this weekend, families are being given the chance of a close-up inspection of one of the Valentine duplex drive amphibious tanks which had been involved in top-secret 'swimming' trials ahead of the D-Day landings.

Now a popular visitor attraction with rowing boats and a passenger launch, Fritton Lake had been the war-time base for British, American and Canadian soldiers trialling floating tanks which would provide vital support for infantry during the Normandy landings which began on June 6, 1944.

The D-Day anniversary weekend is being celebrated with a display of 25 military vehicles, including the Valentine owned by a Midlands enthusiast, slide-illustrated talks and a living history show by a second world war re-enactment group.

There are also boat trips to view the places where the specially-adapted tanks took to the water and came ashore.

Lake manager Stuart Burgess said: 'It's been a great success. We had more than 600 visitors yesterday and at least double that today.'

John Pearson, from Wolverhampton, said his Valentine MK 1X had been cut down and used as a bulldozer after the war. After buying it in 1984 it had become his labour of love to restore it.

He said: 'This could have been one of the ones at Fritton. The trials had to be top-secret because if the Germans had found out, it could have been the end of D-Day.'

Members of the Norfolk Military Vehicles Group in attendance yesterday included Ted and Carol Cole, from Ditchingham, near Bungay, who brought along their post-war US Willys Jeep, and Derek Fulton, of Fritton, near Long Stratton, who displayed his 1944 Willys Jeep.