Cumbria Police closed Michaelson Road Bridge in Barrow-in-Furness on Thursday morning, working in collaboration with BAE Systems, and told residents a further message would be published once the crossing reopened.

The force confirmed the closure at 9am and said the bridge would remain shut while the operation was carried out. An updated statement issued later said: “Michaelson Road Bridge has now reopened. Thank you for your patience.” The closure ran until around 11.40am.

The UK Defence Journal understands that the operation covered the departure of a submarine from the yard, and that the boat involved was HMS Agamemnon, the sixth of the Astute class, with people gathering along the dockside to watch her leave.

Agamemnon was commissioned into the Royal Navy on 22 September last year at a ceremony in Devonshire Dock Hall attended by the King. Around 500 guests were present, and on the same day the King conferred Royal Port status on the town while steel was cut for HMS King George VI, the fourth and final Dreadnought-class submarine.

She completed a three-day trim dive shortly after commissioning, submerging to around 15 metres to confirm the integrity of the pressure hull and to establish her centre of gravity, with crew and engineers moving 16 tonnes of lead weights around the boat to simulate different loading conditions.

Steel was cut for Agamemnon in July 2013 and she was launched in October 2024, making her construction the longest of any nuclear submarine built for the Royal Navy, a delay attributed variously to the pandemic, the diversion of resources to begin the Dreadnought programme and the complexity of the Astute design.

Michaelson Road Bridge carries traffic across the entrance to Devonshire Dock, and closures of this kind are a familiar feature of submarine movements at the yard, with the bridge having to be swung clear before a boat of that size can pass out into Walney Channel.

At 7,400 tonnes and 97 metres, the Astute class carries Spearfish heavyweight torpedoes and Tomahawk Block IV land attack missiles, and the boats protect the deterrent submarines and the carrier strike group while also conducting surveillance and intelligence work. Seven were ordered, with the final submarine, Agincourt, still under construction in the same hall.

Barrow remains the only facility in the United Kingdom with the infrastructure, site licence and resources to design and build British nuclear submarines, and the Defence Nuclear Enterprise annual update to Parliament published this month recorded that the workforce there has grown by more than 1,800 under the current government.

The yard is also preparing for the programmes that follow, with steel due to be cut on the first British SSN-AUKUS submarine in 2027 and the concept design completed earlier this year for SMITE2, a new submarine propulsion testing facility at the site.