The Astute set sail from Barrow for sea trials in
Defence firm BAE Systems is to cut up to 230 jobs at its submarine site in south Cumbria.
The company said it was seeking voluntary redundancies following a review of its workload requirements at the Barrow-in-Furness site.
A spokesman said a 90-day consultation would begin with unions over the "regrettable" job cuts.
Up to 4,500 are employed at the shipyard. The firm also builds heavy artillery at a separate site in Barrow.
John Hudson, managing director at BAE Systems Submarine Solutions, said: "These steps are regrettable but necessary to ensure a sustainable business, thereby allowing the company to deliver to the customer in line with their expectations of value and schedule.
"We have a responsibility to manage our cost base to remain competitive and meet our customers' future requirements."
Keith Hazlewood, national officer of the GMB union, said the job losses had been brought about by the company's decision to slow down the speed of submarine construction.
He said: "This decision is nothing short of short-termism, which is not in the best interests of UK manufacturing, or the community in Barrow or other places that rely on the defence industry for jobs.
"GMB will be seeking a meeting with BAE to explore all means of mitigation against any compulsory job losses."
The Royal Navy's biggest and most powerful attack submarine set sail from the Cumbrian shipyard for sea trials in November.
Measuring nearly 328ft (100m) from bow to stern, Astute is armed with 38 torpedoes and missiles - more than any previous Royal Navy submarine.
Last year, the firm announced it was planning to close three of its UK factories at Telford, Leeds and Guildford with the loss of 500 jobs.