Environmental Impact
Scapa Flow

After the sinking of the 'Royal Oak' in Scapa Flow in 1939, with the loss of 833 lives, it became apparent that more defences were needed to be added to those already in place. A German submarine had entered through one of the shallow sounds between the South Isles. In World War 1 submarine booms had been used to defend Scapa Flow and merchant vessels were sunk in the shallower sounds. The boom defences were improved in World War II and it was not expected that submarines could get through the shallow Sounds. However, events changed all this.

Click here to read a diary account of air attacks on Scapa Flow

The various defences of Scapa Flow, whilst serving a vital purpose during the two World Wars, now have very different purposes. The remains of the WW1 blockships, sunk for the protection of Scapa Flow, between the shallow sounds separating the South Isles, are now used for recreational diving.


Outlook Post
During both World Wars the defence of Scapa Flow became of vital and strategic importance. Apart from the sea defences against submarine attack, many thousands of troops were stationed in Orkney, manning lookout posts and antiaircraft guns. During WW2 up to as many as 40 barrage balloons were in place to force the enemy aircraft to fly higher than they wanted to.

Four barriers, known as the 'Churchill Barriers' were built during World War 2. These barriers link the South Isles on the eastern side of Scapa Flow and were intended to further protect this harbour from enemy submarines. The length, in total, of the barriers is 2.3km and entailed the manufacture of some 66,000 concrete blocks, weighing between five and ten tons each. These were made at St. Mary's, Holm.

Italian POWs were used to build the barriers. They were unhappy, declaring this to be war work, and thus against the Geneva Convention, but were persuaded that the primary purpose of the barriers was to provide an easy means of communication by road for the people living in the south parishes.

In all, 66,662 5-ton blocks were produced for the four Barriers. If laid end to end they would have stretched a distance of about 69 miles.

Work began on the barriers in May 1940, and the channels were effectively blocked by the end of 1942. By 1944 they had been so built up that locals were using a road built over them to drive between the islands – and they are still used as roads today


Henry Ridelaugh

Sandy Wylie

Listen to Civil Engineer,Henry Ridelaugh, describe the construction
of the barriers or to Sandy Wylie who recalls their construction which he witnessed as a boy.