UK arms manufacturer BAE Systems said it was reviewing its warship business but refused to comment on a newspaper report that it was set to close the historic Portsmouth dockyard.
The Sunday Times reported that Portsmouth, on the southeast coast of England, was the likely victim of a sweeping review of the group's shipbuilding operations and a decision was likely in the next three months.
BAE employs about 1,500 workers at the yard and it provides another 1,500 jobs in support roles.
Portsmouth has been a naval base since the 1200s but the first recorded warship built there was the Sweepstake in 1497.
BAE gained a monopoly in the construction of British warships in 2009 when it bought the shipbuilding arm of VT Group, formerly Vosper Thorneycroft.
It has yards on the Clyde in Scotland, at Scotstoun and Govan, and at Portsmouth.
All of the yards are working on sections of the hulls for Britain's two new aircraft carriers, HMS Queen Elizabeth and HMS Prince of Wales.
A company spokeswoman said: As part of our business planning activity, we are reviewing how best to retain the capability to deliver and support complex warships in the UK in the future.
This work is ongoing and we will keep our employees and trade union representatives fully informed, as it progresses.”