8,157-ton nuclear powered submarine leaves UK shipyard for first sea trials

HMS Agamemnon, the Royal Navy’s newest nuclear-powered attack submarine, has left BAE Systems’ Barrow-in-Furness shipyard for the first time. She is heading to HM Naval Base Clyde in Scotland, where she will undergo trials and crew training before joining the operational fleet.

The voyage comes more than 13 years after her keel was laid in July 2013. Although Agamemnon was commissioned in September 2025, she remained at the shipyard while work on her reactor plant and other systems continued.

The submarine is the sixth of seven planned Astute-class boats for the Royal Navy.

A long road to the first voyage

When the submarine’s name was announced in 2013, the UK Ministry of Defence expected her to enter service in 2022. Her first departure from Barrow comes more than four years after that original target.

Agamemnon was rolled out of the shipyard’s Devonshire Dock Hall in October 2024. King Charles III commissioned her into the Royal Navy on September 22, 2025, but the ceremony did not mark the end of testing at Barrow.

Over the following year, work included testing and commissioning her reactor plant and completing other final tasks.

The submarine conducted her first trim dive in October 2025, allowing her crew and builders to assess how she behaved in the water. She has now sailed from the shipyard one year and two days after her commissioning.

Trials before operational service

Once Agamemnon reaches Faslane, she will begin an extensive programme of sea trials, weapons testing and crew training. Leaving the shipyard is a major milestone, but it does not mean the submarine is ready for operational deployments.

HMS Anson, the previous Astute-class submarine, offers an indication of how long the process could take.

Anson left Barrow on February 19, 2023, and subsequently underwent trials in UK waters and at the US Navy’s AUTEC test range in the Bahamas. She became fully operational around June 2024.

A similar timetable would place Agamemnon’s operational readiness in the latter part of 2027.

That remains an estimate: the Ministry of Defence does not disclose planned in-service dates for individual submarines, and Agamemnon’s own trials will determine her progress.

A new boat amid a gap at sea

Agamemnon’s departure follows a period in which no operational Royal Navy attack submarine was known to be underway.

HMS Anson returned from an Indo-Pacific deployment to Devonport on May 27, 2026, and has remained alongside. That left a 120-day gap before Agamemnon sailed, although the new submarine is not yet operational.

HMS Audacious, another Astute-class submarine, is nearing the end of a maintenance period at Devonport and is expected to return to sea in the near future.

At 97 metres long and displacing 7,400 tonnes, Agamemnon carries Spearfish heavyweight torpedoes and Tomahawk land-attack cruise missiles. She is the sixth Royal Navy vessel named for Agamemnon, the legendary Greek king who commanded forces in the Trojan War.

Source: https://interestingengineering.com/military/8157-ton-nuclear-attack-submarine-leaves-uk-shipyard-for-first-sea-trials