Concrete pontoons that were pivotal in the preparations for the D-Day landings are to be given protected status by Historic Scotland.
The surviving elements of the Second World War Mulberry Harbour project on the coast around Garlieston in Dumfries and Galloway are to be listed in recognition of their national importance in the war effort.
The six prototype pontoons, known as "Beetles", were used in sea trials in 1943 to determine their usefulness in launching a military offensive. A year later they played a critical role in the Allied invasion of Normandy.
Olwyn Owen, Historic Scotland's head of scheduling and marine, said: "Garlieston is one of several sites around Britain associated with the Mulberry project, but it was the only place in Britain where extensive sea trials took place.
"The site is the only place in Scotland where physical remains of the Mulberry harbours survive in good condition and in an accessible location."
Built in Motherwell, the pontoons belong to a floating harbour prototype designed by the War Office and tested at Garlieston.
Although the harbour was wrecked during a storm in the 1940s, all six pontoons survived in good condition and retain a high degree of their original character.
"The Garlieston remains are considered to have international historic significance as the Mulberry harbour project played an integral role in the success of the Allied invasion of Normandy in 1944," said Owen.
"The remains at Garlieston represent a tangible link to one of the most remarkable feats of military engineering pioneered during the Second World War."