Off the Coast of Scotland, UK — September 25, 2026
Thirteen years in the making, the Royal Navy's newest and most advanced attack submarine has finally left the shipyard and hit open water — a milestone moment for a vessel already being hailed as one of the most powerful submarines Britain has ever built.
Meet HMS Agamemnon
HMS Agamemnon (S124), the sixth Astute-class submarine built by BAE Systems, departed the company's Devonshire Dock Hall shipyard in Barrow-in-Furness to begin her initial sea trials — a critical testing phase ahead of officially joining the active fleet. She's now making her way toward HM Naval Base Clyde (Faslane) in Scotland, the home of the UK's submarine force, where an extensive program of sea trials, weapons testing, and crew training will continue.
Nicknamed "Awesome Aggie" by her crew, the submarine is a serious piece of engineering: 97 meters long, displacing 7,400 tonnes, and powered by a Rolls-Royce nuclear reactor that means she'll never need refueling throughout her entire 25-year service life. She's armed with heavyweight Spearfish torpedoes and Tomahawk land-attack cruise missiles capable of striking targets more than 1,000 miles away.
Her keel was laid all the way back in July 2013, and she was formally commissioned into the Royal Navy by King Charles in a ceremony last September — meaning this departure marks the end of a genuinely long journey from steel to sea.
Why This Matters for Britain's Defence
First Sea Lord General Sir Gwyn Jenkins called the milestone a significant moment for national security, describing sea power as fundamental to keeping the country and its people safe amid what he called an increasingly dangerous world. He emphasized that Agamemnon represents one of the most advanced submarines ever operated by the Royal Navy.
Defence Secretary Wes Streeting echoed that sentiment, framing deterrence as the bedrock of Britain's national security and noting that having toured the boat and met her crew firsthand, he sees her entry into service as a major step in strengthening the UK's warfighting readiness and NATO's collective defence.
A Fleet That Needed Reinforcements
The timing carries extra significance: Agamemnon's departure comes after a period during which no operational Royal Navy attack submarine was known to be actively at sea. Sister submarine HMS Anson had just returned from an Indo-Pacific deployment in late May and remained docked, leaving roughly a 120-day gap in deployable attack-submarine coverage — though Agamemnon herself isn't yet combat-ready. Another Astute-class boat, HMS Audacious, is nearing the end of a maintenance period and expected to return to sea soon as well.
What Happens Next
Leaving the shipyard is a major milestone, but it's far from the finish line — Agamemnon still faces months of trials, weapons testing, and training before she's considered fully operational. For comparison, sister submarine HMS Anson took roughly two years between leaving her own shipyard and eventual deployment, including testing at the US Navy's AUTEC range in the Bahamas.
The submarine's arrival also builds on the UK's broader commitment to continuous submarine production, part of a defence investment push worth an estimated £47 billion over the next four years.
This is a developing story. The Ministry of Defence does not disclose planned in-service dates for individual submarines, so Agamemnon's exact timeline to full operational status will depend on how her trials progress.