FOR decades, in the teeth of storms, gales and raging seas, it has stood guard on a lonely vigil but now the historic Nab Tower, the vital aid to navigation in the Solent, is to undergo a major upgrade.

Perhaps not the most glamorous or elegant of structures, the Nab Tower has played a key role in Hampshire’s maritime heritage.

Now urgently needed maintenance work will secure the tower’s future and ensure the continuation of its highly important role in the decades ahead.

The task will be carried out by Trinity House, the country’s official lighthouse authority, which also provides aids to navigation to assist the safe passage of a huge variety of vessels through some of the busiest sealanes in the world.

The Nab Tower has been gradually deteriorating following almost a century of battling the elements and in recent years this wear and tear has increased to an unacceptable and dangerous degree.

At present the helicopter pad is offlimits and boat access is almost untenable due to the poor condition of the external superstructure.

Trinity House has commissioned a project to extend the structure’s lifespan by at least 50 years, by reducing the structure’s height, removing all external steel and cladding the existing concrete sub-structure in concrete.

Nab Tower is located in the eastern approaches to the Solent and was originally built as a defensive structure for the Admiralty in 1918, but became redundant when the First World War ended.

Trinity House occupied part of the tower from 1920 onward, installing a light to replace the Nab light-vessel, with the structure remaining under the control of the Ministry of Defence (MoD).

The station was staffed as an offshore lighthouse, with three keepers who were relieved monthly, until the lighthouse was automated in 1983.

The MoD built the helicopter deck and internal reinforced concrete caisson prior to Trinity House acquiring the freehold in 1984.

Once completed, the remodelled Nab Tower will be a state-of-the-art navigation aid and result in reduced maintenance costs as the station will be able to be attended by Trinity House vessels without the need for a helicopter.

The work will be completed in the summer of 2013 with a break over the winter to avoid the seasonal weather.

This light is responsible for guiding ships of all sizes and nationalities into the deep water channel for Southampton and Portsmouth.

The story of its strange origin goes back to the early part of 1918 when attacks by German U-boats on Britain’s merchant fleet were causing the Admiralty so much anxiety that it was decided to take strong, if unorthodox, counter measures and a startling plan was drawn up by backroom scientists.

This was to sink a line of eight, fort like towers, each costing £1m, across the straits and to link them with steel boom nets, with the idea of closing the English Channel to enemy ships.

About 3,000 civilian workmen were brought to a quiet backwater in Sussex and work began almost at once on two of these towers, each 40 feet in diameter with latticed steelwork surrounding the 90ft cylindrical steel tower and built on a hollow 80ft thick concrete base designed to be flooded and sunk in about 20 fathoms.

One tower was completed when the war finished, and the other half-completed giant was broken up for scrap.

After much thought it was decided to use the solitary “white elephant’’ to replace the old Nab light vessel by sinking it at the eastern end of the Spithead approaches, also serving as an invaluable naval defence post if required.

On a calm day in 1920 two paddle wheel tugs towed the tower to a position near the light vessel. There were many anxious moments as the base was opened to the sea, but it performed exactly as planned, settling without incident, and kept steady by the immense volume of water inside the base.