THE colossal crane which has towered over Devonport dockyard for 25 years will be taken down this autumn in one of the biggest engineering operations the city has ever seen.

Six hundred workers will be 'evacuated' from the area around the Submarine Refit Complex while the refuelling crane is dismantled.

The crane, a landmark feature of Plymouth's skyline, is the biggest in Western Europe. But it is no longer needed, and will be removed in a painstaking process which will be visible from just about everywhere in the city.

The crane will be replaced by a low-level reactor access house and rail track as part of a new £150million facility which is being built for defuelling decommissioned nuclear-powered submarines.

World-class Dutch heavy lifting specialist Mammoet has been brought in to handle the project in September and October.

The firm, whose name means 'mammoth' in Dutch, was involved in raising the stricken Russian nuclear submarine K-141 Kursk from the Barents Sea in 2001.

As part of the crane removal project, a gigantic metal tower is currently being built in sections in Holland.

It will be brought to Plymouth and erected next to the crane's 46-metre high plinth at 15 Dock.

Two beams will then be installed to connect the tower and plinth.

The crane's massive jib will be 'jacked up' and put on 'skids' and then slowly slid across inch by inch to the top of the tower.

The 1,400 ton jib, more than 100 metres long, will then be winched down from the tower using steel cables and hydraulics, in a process known as strandjacking.

The jib will be lowered onto a barge and floated away to another part of the dockyard site.

The metal tower will then be dismantled, but the crane's concrete plinth will remain, because it contains water tanks which can still be used by the dockyard.

Roger Hardy, managing director submarines for Babcock Marine (Devonport), called the project “a huge evolution”.

He said the firm would not be revealing the exact day when the delicate project would begin, because “we do not want the team to have any pressure”.

“Safety is key,” he stressed. “Many of you will see it happening within the next eight to 12 weeks.”

A year ago, The Herald reported how more than £150million was being pumped into the dockyard to create the facility for defuelling decommissioned nuclear-powered submarines.

Hundreds of jobs will be safeguarded by the MoD contract.

About 500 people will be involved in building the facility, and about 250 in the long-term defuelling programme. It will enable the MoD to restart its programme of de-fuelling nuclear-powered submarines in 2012.

The modernisation will also upgrade the defuelling capability to meet modern nuclear design standards.