The Churchill Barriers: Orkney’s Wartime Causeways, Scotland

Drive south from Kirkwall today and you cross four low causeways strung between islands that were, until 1945, separated by open water. The Churchill Barriers were built in wartime secrecy to seal Scapa Flow against German U-boats, using thousands of tonnes of concrete, scuttled blockships and the forced labour of Italian prisoners of war. What began as an urgent naval defence project quietly reshaped Orkney’s geography — linking South Ronaldsay, Burray, Glimps Holm and Lamb Holm to the Mainland for good. Travellers on Odyssey Traveller’s Scottish Isles small group tour stop to view the barriers and the Italian Chapel during their days on Orkney, and the story behind the barriers says as much about Orkney’s strategic importance as any of its Neolithic sites.

Why Churchill Ordered the Barriers

Scapa Flow, the broad natural harbour enclosed by Orkney’s southern islands, had anchored the British fleet since the First World War. Its size and shelter made it ideal for the Home Fleet — but the shallow eastern channels between the islands were never fully blocked, relying instead on sunken ships and anti-submarine nets. On the night of 14 October 1939, German submarine U-47 slipped through one of these gaps and torpedoed HMS Royal Oak at anchor, killing 835 men. The loss, only weeks into the war, was a considerable blow to naval confidence and to Winston Churchill personally, then First Lord of the Admiralty.

Churchill’s response was direct: permanently close the eastern approaches to Scapa Flow. Rather than rely on nets and old blockships that could shift or be evaded, the Admiralty ordered solid causeways built across the four channels — Kirk Sound, Skerry Sound, East Weddel Sound and Water Sound — connecting Mainland Orkney to Lamb Holm, Glimps Holm, Burray and South Ronaldsay in turn. Work began in May 1940, under wartime urgency and considerable engineering uncertainty about how concrete would behave in fast tidal currents.

Building the Barriers: Blockships, Concrete and Italian Labour

The first stage followed established practice: obsolete ships were deliberately scuttled in the channels to slow the current and provide a rough foundation. Some of these blockship hulls are still visible today, rusting quietly beside the modern causeways — a detail easy to miss from a moving coach but worth pointing out to fellow travellers as you cross.

Onto this foundation, engineers poured huge concrete blocks — weighing five or ten tonnes each — dropped into place from overhead cableways before being locked together with rubble core and a concrete cap. It was slow, dangerous work in strong tidal water, and Orkney’s civilian workforce alone could not supply the labour needed at wartime pace.

From January 1942, around 550 Italian prisoners of war, captured during the North Africa campaign, were transported to Orkney and housed in a camp on Lamb Holm. Under the terms of the Geneva Convention, prisoners could not legally be made to work on projects of direct military value, so the barriers were officially recorded as improving civilian transport links between the islands — a technicality that let construction continue without international objection. It is this same camp of Italian prisoners who, in their limited free time, converted two Nissen huts into the ornate Italian Chapel, still one of Orkney’s most visited sites and a striking counterpoint to the barriers’ purely functional concrete.

Engineering Four Causeways Against the Tide

What makes the Churchill Barriers a genuinely interesting piece of engineering, rather than simply a wartime footnote, is the scale of the problem the builders faced. The channels between the islands carry strong tidal streams, and early attempts to place concrete blocks by crane from barges proved too slow and imprecise. Engineers instead built cableways strung across each sound, allowing wet concrete to be poured directly into wooden frames or pre-cast blocks that were lowered with far greater accuracy. By the time the barriers were substantially complete in 1944, roughly 250,000 tonnes of rock and concrete had gone into the four causeways — a very large undertaking for islands with a small resident population and limited existing infrastructure. The barriers were formally opened on 12 May 1945, days after the war in Europe ended, by which point their original military purpose had already been overtaken by events. What they left behind, however, was permanent: a road link between islands that had previously depended entirely on small boats.

The Barriers Today: Roads, Beaches and a Changed Coastline

The barriers now carry the A961 road, making it possible to drive from Kirkwall to South Ronaldsay in well under an hour — a journey that would once have required several separate ferry crossings. For Odyssey Traveller’s guided exploration of Orkney’s Neolithic landscape, this matters practically as well as historically: the day the group visits the Barnhouse Neolithic Village and the Earl’s Bu at Orphir ends by crossing the causeways that once protected the fleet to reach the Italian Chapel on Lamb Holm. Ferries still matter for the longer journeys: our guide to NorthLink ferries to Orkney and Shetland covers the overnight crossing the tour takes from Kirkwall to Lerwick.

One unplanned effect of the barriers has been geological. By slowing the tidal flow through the sounds, they allowed sand to accumulate on their western sides, creating small beaches that did not exist before the war — Orkney’s version of a coastline still quietly rearranging itself eight decades on. On a clear day, it is worth stopping partway across to look out over Scapa Flow itself and imagine the scale of the fleet it once sheltered, and the single submarine that slipped past its defences in 1939.

Seeing the Barriers as Part of a Wider Story

Visited in isolation, the Churchill Barriers can look like little more than a road connecting a scatter of quiet islands. Seen alongside the Italian Chapel, Scapa Flow and the wartime remains scattered across Orkney’s southern isles, they become part of a much richer account of how a remote archipelago was drawn into a global conflict — and how prisoners with almost no resources built something of lasting beauty in the middle of it. That contrast, between grim necessity and quiet ingenuity, is part of what makes this corner of Orkney worth more than a passing photograph from the coach window.

For travellers with an interest in twentieth-century history alongside Orkney’s much older past, the barriers are a reminder that this is a working, changing landscape rather than a museum piece — and that some of its most significant transformations happened well within living memory. Odyssey Traveller’s guided route through Scotland’s islands, from Arran to Shetland, sets this wartime chapter alongside Orkney’s Neolithic sites and Norse heritage, giving the barriers proper context rather than a brief mention in passing.

A short causeway crossing rarely gets much attention in a travel itinerary, but the Churchill Barriers reward a closer look — for the engineering, for the history of Scapa Flow, and for the story of the men who built them under circumstances few would choose. Odyssey Traveller’s small group tour gives you the time to stop, look properly, and hear that story from a local guide rather than glimpsing it through a coach window on the way to somewhere else.