Nab Tower – Mystery Tower 1

During the First World War, the British Admiralty designed eight towers codenamed M-N that were to be built and positioned in the Straits of Dover to protect allied merchant shipping from German U-boats. Designed by civilian Guy Maunsell, the towers were to be linked together with steel nets and armed with two 4-inch guns with the idea of closing the English Channel to enemy ships.

The first Mystery Tower in 1922 as the Nab Tower. ©Alan Humphries Collection

However, by the end of the war in 1918 only one such tower had been completed, at the then-cost of one million pounds, and was located in Shoreham Harbour, awaiting deployment. While another part-built tower would eventually be dismantled in 1924, there remained the completed 92-foot-tall metal cylinder sitting on a raft of concrete.

In 1920 the completed tower was towed by two paddle-wheel tugs to the Nab rock, a rock in the deep-water approach to the eastern Solent and previously marked by a lightship. Buoyancy was provided by the honeycomb construction of the concrete base, creating 18 watertight compartments. When these were flooded, the structure sank and settled to rest at an angle of 3 degrees from vertical towards the northeast – a characteristic tilt which is obvious to this day.

The story of the construction of the two mystery towers:

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