Looking at the island now it is hard to imagine the hive of activity that went on during the world wars. Recent heavy weather uncovered a sign of just one part of that activity.
During both wars the purpose of the Isle of May was for observing. Records are unclear but it seems that there were hardly any or no guns on the island but a whole range of different ways of watching, primarily to guard the entrance to Britain’s most important wartime dock at Rosyth. U-boats were a huge threat to the ships using the Forth and the Isle of May was the gate at the entry to the forth but how do you guard and 15 mile gate from underwater attackers. The answer is with an indicator loop. This was a metal cable laid along the sea bed from Crail to North Berwick and running through a control room on the island. This building was built opposite the Assistant Keepers cottage in Fluke Street and housed a simple mechanism that indicated whenever a metal hulled boat moved over the cable. A 24 hour watch was held in the building with local boats having to phone in to get permission to pass in or out of the Forth. Apparently fishing boats were apt to forget causing all sorts of false alarms but for the whole time of the war no enemy surface ships or submarines broke into the Forth.
Much of the cable on the island was removed after the war and the brick part of the building was finally demolished in 2004 but parts of the armoured cable can still be seen and down at Pilgrims Haven some of the bad weather have exposed the cable as it runs down under the shingle and into the sea (see photos).
Much more can be found about indicator loops from Richard Walding’s website and Ron Morris’s book “Aboard HMS May Island – The Story of May Island’s Role in Wartime.”