HMS Ambush (S120): A Nuclear Hunter-Killer From Barrow to Brazil

Barrow-in-Furness-Built

HMS Ambush was built by BAE Systems Submarine Solutions at Barrow-in-Furness, ordered in March 1997 and laid down in October 2003, a long gestation typical of the complex Astute-class programme. She was launched on 6 January 2011 and commissioned on 1 March 2013 at HM Naval Base Clyde, the second of the Royal Navy's Astute-class nuclear-powered attack submarines.

A Reactor That Never Needs Refuelling

Ambush is powered by a single Rolls-Royce PWR2 nuclear reactor fuelled with highly enriched uranium, designed to run for her entire 25-year service life without ever needing to be refuelled, a remarkable piece of engineering that lets her stay submerged and on station for as long as her crew's supplies and endurance allow.

The phrase highly enriched uranium is doing quiet work in that sentence and is the reason she never needs refuelling. A civil power station runs on uranium enriched to a few per cent, and it is refuelled every couple of years, which is fine for a building. A submarine cannot be opened up like that: getting at the core means cutting into the pressure hull, which is a multi-year dockyard job. Britain's answer has been to enrich the fuel far more heavily, so that a single core carries enough energy for the whole of a boat's twenty-five-year life. France went the other way, using low-enriched fuel and accepting that her submarines must be refuelled periodically. There is no free choice in it: the British approach buys availability and pays for it in the sensitivity of the material and the difficulty of eventually disposing of it, which is the problem now sitting in two dockyard basins full of laid-up boats.

She carries six 21-inch torpedo tubes capable of launching up to 38 weapons between them, including long-range Tomahawk Block IV cruise missiles and Spearfish torpedoes.

Maiden Deployment to Brazil

Ambush's maiden overseas deployment in October 2014 took her to the United States and Brazil, calling at Port Canaveral and taking part in celebrations marking the centenary of the Brazilian submarine force, a particularly fitting piece of naval diplomacy for a brand new boat. She went on to take part in Exercise Joint Warrior and Exercise Dynamic Manta in 2015.

Ambush is one of the better submarine names the Royal Navy has, and it has only been used twice: once for an Amphion-class boat completed in 1947 and scrapped in 1971, and once for this one. It describes the job exactly. A submarine does not fight in the way a frigate does, by finding an enemy and closing with him; she waits where he is going to be, unseen, and the entire value of her lies in the fact that he does not know she is there until she chooses otherwise. Everything about the design, the reactor that never has to surface and the enormous care taken over noise, exists to make an ambush possible.

A Collision Off Gibraltar

On 20 July 2016, while surfacing during exercises in the Strait of Gibraltar, Ambush collided with the Panama-flagged merchant vessel Andreas, sustaining significant damage to the top of her fin, where much of her sonar equipment is housed.

Repairs cost some £2.1 million, and her commanding officer forfeited a year's seniority for negligently hazarding the vessel, a costly reminder of just how crowded and hazardous the waters around Gibraltar can be for a submarine coming up to periscope depth.

The circumstances are more interesting than that summary suggests. Ambush was running the Submarine Command Course at the time, the Perisher, and a student had her at periscope depth practising exactly the thing the course exists to teach: holding a picture of the shipping above you while remaining unseen. A small yacht appeared and the avoiding action taken to clear it put the submarine onto a collision course with a merchant ship. The court martial found that Teacher, the instructor who is legally in command throughout, had been concentrating on his students rather than independently building his own picture of the surface, and had assumed the man at the periscope had it in hand.

The Strait of Gibraltar is about the worst place in Europe to make that mistake. It is nine miles across at the narrowest point and carries a very large share of the traffic entering and leaving the Mediterranean, with ferries crossing the flow and small craft everywhere in summer. A submarine at periscope depth there is looking through a tube a few inches wide at a great deal of shipping moving in several directions, with only a few seconds of exposure at a time. The damage was to the top of her fin, which is where most of her sonar lives, and that is why it cost £2.1 million rather than the price of a dent.

She is the third Royal Navy submarine to come to grief with the Perisher running. HMS Trenchant sank the trawler Antares off Arran in 1990 immediately after finishing a Perisher exercise, with four men killed. HMS Trafalgar went aground at Fladda-chuain during one in 2002. Ambush hit a merchant ship during one in 2016. Three incidents across twenty-six years of continuous training is not an indictment of the course, and it would be unfair to present it as one: the course exists because putting a submarine among surface traffic at periscope depth is the most demanding thing a submariner ever does, and it is done under an instructor precisely so the errors happen where somebody senior can catch them. Sometimes he does not catch them. What the course actually demands is set out in HMS Oracle.

Ongoing Service

By mid-2026 Ambush's absence from the water had become part of a larger story than her own maintenance schedule. She had not been to sea since autumn 2022, and by June 2026 was reportedly being cannibalised for components at Faslane to keep her sister boats seaworthy rather than working toward a return of her own.

That month, all five of the Royal Navy's Astute-class boats, HMS Astute, HMS Ambush, HMS Artful, HMS Audacious and HMS Anson, were alongside at the same time: HMS Astute deep into a multi-year refit at Devonport that began in June 2025, HMS Artful last at sea in the spring of 2023, and HMS Audacious having spent the better part of two years waiting for dock space before finally getting into No. 15 Dock in February 2025.

With the last Trafalgar-class boat, HMS Triumph, decommissioned in July 2025, the fleet no longer has a spare hull to absorb a long refit without leaving Britain's attack-submarine capability critically thin, turning what might once have looked like one boat's bad luck into a fleet-wide readiness problem.

This is a live article which will be updated when more information is available.