THE Devonshire Dock Hall was unveiled in 1986 and remains the second largest indoor shipbuilding construction complex of its kind in Europe.

Back in 1977, Vickers bosses first mooted the idea of a Submarine Facilities Project – a covered complex for building submarines and surface vessels.

The complex would have a shiplift which could gently lower vessels into the water and end the need for dynamic launches, which saw vessels being released down a ramp (launchway) into the channel.

Boats now move out of the hall at a speed of one metre per minute.

The new hall was designed by RT James and Partners – a task which required innovative construction methods.

The main contractors, Alfred McAlpine, had to lay a concrete floor at a depth of six and-a-half feet on more than two million tonnes of compacted sand.

The sand was transported from Roosecote and the concrete foundation piles are nearly as deep as Nelson’s Column.

Up to 1,700 cubic yards of concrete were poured every day during construction by the 764 workers employed by McAlpine. The shifts covered 16.5 hours every day.

The steel shell of the hall took nine months to complete and miles of cable were laid in underground passageways eight feet wide and eight feet deep.

The shiplift’s platform – more than 500 feet long, was installed in just 23 days.

The structure has a maximum load of 24,300 tonnes and was suspended from 108 electric winches, which are operated from a central control.

The platform was designed to allow vessels to be brought into the dock and manoeuvred over the shiplift while the platform is below water level.

The winches then bring the vessel up to the level of the quay.

The complex covers an area of 40,000 square feet. The massive doors, which open to allow new submarines to be moved into the dock, are 29 metres high.

The DDH, which cost £230m to build, has not gone unnoticed as an engineering success.

In 1988, environment secretary Nicholas Ridley highly commended the submarine hall in the civil engineering section at the British construction industry awards.

The hall was hailed as a project whose “vast loads, huge enclosed space and complexity of production facilities was beyond UK experience”.

This Saturday will mark 25 years to the day that the DDH was unveiled.

On September 3, 1986, the then prime minister, Margaret Thatcher, officially opened the DDH, with the Vanguard submarine providing a dramatic backdrop.

The bulding’s name is taken from the dock in which it was built; Devonshire Dock was opened on September 19, 1867 – at the time a massive feat in itself.

At 51 metres high, 265 metres long and 65 metres wide, the DDH was the largest indoor shipbuilding structure in Europe. This record has since been broken by IHC Merwede’s shipbuilding hall in the Netherlands, but only just.

The Dutch shed is 264 metres long, 97 metres wide and 51 metres high.

But the Barrow hall’s capabilities and achievements continue to impress.

Current managing director of BAE Systems Submarine Solutions, John Hudson, said: “Devonshire Dock Hall was a remarkably far-sighted development by the company 25 years ago, and the fact that it looks now largely as it did when it was opened by Mrs Thatcher on September 3, 1986, shows that the facility has more than stood the test of time.

“Sound concept design, with inbuilt flexibility, is the key to the hall’s longevity, and the benefit it has brought to the business.

“The construction of the hall on reclaimed land, providing good access, and the layout of the building have proven to be effective design solutions.

“The hall’s flexibility is demonstrated in the range of vessels that have been built there – some of the most advanced and capable vessels ever operated by the Royal Navy – from the Vanguard class Trident submarines, to surface ships such as the Auxiliary Oilers and amphibious assault ships, to the current Astute-class nuclear powered-attack submarines.

“In building these ships, we have evolved strategies that could never have been imagined when the hall was built – such as constructing giant modules off the boat, in workshop conditions, and then shipping the completed module into the ship’s hull.

“We are now looking forward to building the next class of deterrent submarines to replace the Trident boats, and they will represent another advance in engineering achievement.

“The DDH has, over the last 25 years, become an iconic symbol of the company, the town and Barrow shipbuilding.”