Churchill Barrier No. 4

Churchill Barrier No. 4 is a 650m-long causeway, part of a group of four 'Churchill Barriers' constructed between 1940 and 1944. These barriers were built to link islands at the eastern side of Scapa Flow and to prevent access from the east into the channels leading to the main British naval base. The scheme was designed and supervised by Sir Arthur Whitaker, the Admiralty's Civil Engineer-in-Chief, with Balfour Beatty & Co Ltd as the contractors, and a workforce that included Italian prisoners of war interned at Lamb Holm. Originally conceived as defensive structures to prevent ships and submarines from entering Scapa Flow, the barriers now provide road access southwards from Mainland to South Ronaldsay and link Burray with South Ronaldsay.

The barriers were built with a base constructed using wire cages or baskets filled with broken rock, dropped into the channel and largely below water level. A road carriageway is formed from dumped aggregate and horizontally laid concrete blocks over this base. To protect the causeway core and prevent tidal overtopping, five and ten ton cast concrete blocks were placed at varying angles on either side of the barrier. The construction of all four barriers involved approximately 250,000 tons of stone rubble and 66,000 concrete blocks. Churchill Barrier No. 4 now carries the A961 road south to South Ronaldsay, and the barriers are numbered from north to south. Excluded from the listing are a concrete edge beam, crash barriers, modern road surfacing, a car parking area, and a toilet block to the northeast.