Churchill Barrier No. 3

Churchill Barrier No. 3 is a 420-meter long causeway that is part of a group of four barriers built between 1940 and 1944 to connect islands on the eastern side of Scapa Flow. These solid causeways were designed to prevent access from the east into the channels leading to Scapa Flow, which served as the main British naval base during the Second World War. The project was overseen by Sir Arthur Whitaker, the Civil Engineer-in-Chief of the Admiralty, and constructed by Balfour Beatty & Co Ltd, with the help of Italian prisoners of war interned at Lamb Holm who made the concrete blocks and built the structure.

The barriers were intended to stop ships and submarines from entering Scapa Flow, while also providing road access from Mainland to South Ronaldsay. Barrier 3 connects Glimps Holm and Burray. Although they were built during a time of national crisis, their ongoing purpose is to serve as causeways and roads linking the islands.

The construction of Barrier 3 includes a base made from bolsters, wire cages filled with broken rock, which were submerged in the channel. Most of the base is underwater. The road surface consists of dumped aggregate and horizontally laid concrete blocks. To protect the core of the causeway and prevent tidal overtopping, five-ton cast concrete blocks are positioned at angles on either side of the barrier. In total, the four barriers required approximately 250,000 tons of stone rubble and 66,000 concrete blocks. Currently, the barriers support the A961 road leading south to South Ronaldsay and are numbered from north to south.