The eccentric engineer

E&T tells the story of the Shoreham Towers - one of the British Admiralty's greatest engineering secrets.

Everybody likes a mystery, provided they're not paying for it, and few in engineering terms have been as strange or as costly as the story that began in June 1918 with the arrival of a detachment of Royal Engineers at Southwick Green in Sussex.

The work party that summer were all sworn to the utmost secrecy as they set about building a camp to house the staff for project 'M-N'. Not long after, the locals in Shoreham noticed that a huge construction had begun on their doorstep as two gargantuan concrete-and-steel towers began to rise from the harbourside laboured on by over 3,000 men, mainly at night.

It being wartime, the nature of these towers was, of course, secret but their presence could hardly be hidden. Each tower stood on a hollow, 80ft-thick concrete base, and the 40ft-wide, 90ft-high, 1,000t steel column that emerged was surrounded by a lattice of steelwork.

By the autumn of 1918, the towers were visible from as far away as Beachy Head and were known as the 'Shoreham Mystery Towers'. They caused speculation in the press as far afield as New York with people wondering just what these enormous structures might be for.

Back in the Admiralty in London, the purpose of the mystery towers was, of course, known but that does not mean there wasn't still a great deal of speculation. The towers were costing well over £1m each (or, using average earnings for comparison, £172m in modern terms) and eight (some sources say 12 and one even 16) of these towers were planned. There was some doubt that the rest could even be afforded.

But what were they for? Project M-N had been initiated by Sir Alexander Gibb, who was engineer-in-chief to the Admiralty. Gibb had engineering in the blood - indeed, the profession was so ingrained in him he might as well as have oil for blood. His father was the founder of the engineering group that would become Easton Gibb and Son, his grandfather had been a pupil of Telford, his great-grandfather was a founder member of the Institution of Civil Engineers, and his great-great-grandfather was a contemporary of Brindley and Smeaton.

He had worked as resident engineer on the Whitechapel extension to the Metropolitan line before the First World War. He had overseen the construction of Rosyth naval base before being appointed chief engineer, ports construction, to the British armies in France in 1916, with special responsibility for rebuilding the railheads and ports that might be destroyed by retreating Germans. Then, in 1918, he had come to the Admiralty where his fabulously expensive towers were causing something of a headache.

Gibbs' plan was typically bold. With the brilliant but untrained Major John Reith (later Lord Reith, first director general of the BBC) as his assistant, he intended to counter the menace of German U-Boats in the simplest but most dramatic way.

A chain of huge towers would be placed across the English Channel from Dungeness to Cap Gris Nez, each linked to the next by steel anti-submarine nets, effectively closing off the whole of the world's busiest seaway to the U-Boats.

Each tower would have a steel superstructure containing gun emplacements and room for 100 troops to man each lonely outpost. The towers would be equipped with submarine detection equipment run off their own generator. Any U-Boat foolish enough to try to enter the Channel would get caught in the nets and be either sunk or detected and disposed of by the tower crews.

It was undoubtedly one of the most ambitious engineering plans of the war but it was a plan too late, much to the relief of the Admiralty accountants who were looking at a £2bn bill (in modern terms) to complete the project - enough to sink a few battleships, or perhaps float a bank.

On 11 November 1918, with Tower 1 just nearing completion, the war ended and the behemoths became redundant overnight. Tower 2 was eventually broken up for scrap in 1924, a task which took nine months - longer than it had taken to build the giant - but Tower 1 is still visible today as a new life was found for it.

In early September 1920, the honeycomb-structured concrete base was pumped free of water and the 30,000t structure rose from the Shoreham seabed.

On 12 September, the Tower was towed out of Shoreham harbour by Admiralty tugs, only just clearing the harbour walls. After a journey of 41 miles, which took them to the Nab Rock off Bembridge on the Isle of Wight, the tower was tethered and the seacocks in the hollow base opened. Slowly the tower began to sink, coming to rest on a sand bank at a jaunty angle of 3° from vertical. Not surprisingly for a 30,000t structure, that is exactly where it remains to this day. 

The new Nab Tower lighthouse was now in place, and the four crewmen of the old Nab Rock lightship were transferred to their new high-tech, multimillion pound home. Solar-powered and unmanned, Tower 1 still serves as the Nab light and as a reminder of what was once the Admiralty's greatest secret.

Justin Pollard's latest book, "Wonders of the Ancient World. Antiquity's greatest feats of design and engineering" is published by Quercus at £20.00


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