More than 700 jobs are being lost at the Barrow base of BAE Systems, the company has said.
Hundreds of people have already lost jobs at the Barrow yard
The defence giant is to axe 760 jobs, mainly at the Cumbria shipyard which
Up to 720 of the losses will be in Barrow, where 3,000 workers are employed building naval ships and submarines.
But unions have criticised the move, saying it will have a devastating effect on the region.
The company said it needed to match its resources to its current and future
The firm also wanted to establish and maintain a competitive cost base.
A company spokesman said: "These steps, while regrettable, are necessary and will ensure the creation of a sustainable business, thereby allowing the company to deliver to the customer in line with their expectations of value."
Murray Easton, managing director of BAE Systems Submarines, said the announcement was "regrettable" but he added the cuts were vital to make sure that the company improved its design and build of the Astute submarine and to deliver it on time and to cost.
He said: "This is very difficult and disappointing news for the employees, their families and the local community."
Union leaders branded the job losses a "devastating blow" to Cumbria and have pledged to oppose compulsory redundancies.
Keith Hazlewood, national officer of the GMB union, said: "The entire community will feel the impact of these job losses. The job cuts are devastating to the manufacturing sector, UK ship building and the region."
The GMB said it was seeking an urgent meeting with the company to try to mitigate the losses.
John Wall Amicus national officer for shipbuilding said: "UK shipbuilding is being sliced up like a salami, with the result that thousands of skilled craftsmen, designer and engineering workers leaving the industry in the UK to work for foreign competitors.
"This is not acceptable to Amicus, we will be seeking urgent meetings with BAE Systems to discuss this matter."
Managers at the Barrow shipyard had said jobs could be lost unless new contracts were won.
In 2003, amid hundreds of job losses, BAE Systems announced Barrow was to become a submarine only yard.
The yard is currently building three late-running and over-budget Astute submarines for the Royal Navy.
But no further orders are in the pipeline.