The sixth Astute-class attack submarine, HMS Agamemnon, is still completing the final stages of its in-water commissioning before being handed over to the Royal Navy for sea trials, the Ministry of Defence has said.
The update was provided by Defence Minister Luke Pollard in response to a written parliamentary question from Conservative MP Ben Obese-Jecty, who asked whether delays identified in the National Infrastructure and Service Transformation Authority’s Major Projects Annual Report had affected the in-water phase for Boat 6.
Pollard did not state directly whether the delays had changed the planned duration of the in-water phase, but confirmed the submarine’s current position in the programme.
He said: “In September 2025, the sixth Astute Class submarine, HMS AGAMEMNON was commissioned into the Royal Navy and is undertaking the final stages of her in-water commissioning, before a handover to the Royal Navy to undertake sea trials.”
Agamemnon was commissioned into the Royal Navy in September last year but has remained with the build and commissioning programme while work continues ahead of sea trials. In-water commissioning covers the period in which systems are progressively tested and prepared after the submarine has left the construction hall and entered the water.
Pollard also provided an update on Achilles, the seventh and final Astute-class submarine, which remains under construction at BAE Systems’ Barrow-in-Furness site. He said: “Achilles, the seventh and last boat of the class, remains at an advanced stage of build in Barrow-in-Furness and work to recover from the impact of the fire in the Devonshire Dock Hall is progressing well.”
The fire in the Devonshire Dock Hall affected the site where the final Astute-class submarine is being completed, requiring recovery work while construction continues.
Achilles will complete the seven-boat Astute programme, following HMS Astute, Ambush, Artful, Audacious, Anson and Agamemnon. The nuclear-powered attack submarines are designed for anti-submarine warfare, anti-surface warfare, intelligence gathering and land-attack missions. Asked in effect whether the programme’s schedule had shifted, the MOD again declined to disclose the planned in-service dates of the submarines.
Pollard said: “The planned in-service dates for Royal Navy submarines are withheld as disclosure would, or would be likely to, prejudice the capability, effectiveness, or security of the Armed Forces.”
At least they have good names.
The Russian submarine threat to the UK is centred on about 10 active SSN. Of these, maybe half could be considered ‘modern’. The remainder are relics of the Cold War, and a less of a problem (but not neutered by age).
Now, to combat that, the UK needs rough numerical parity. A fleet of 10 SSN would be capable of fending off the Northern Fleet. The government has pledged for 12 boats, which would probably be overkill for the Atlantic mission.
Assuming 50% availability (once the upgrade programmes to infrastructure are complete), the RN could task three submarines to the North Atlantic, one submarine to the carrier strike group, and one submarine to Australia and the Indo-Pacific. If 12 are procured, you can now task a second submarine to Australia.
That’d be rough parity to a wartime Northern Fleet SSN capability (the carrier-tasked submarine would likely be diverted to the North Atlantic alongside the carrier herself), produced by the RN alone. In reality, there’d be a number of Canadian, Norwegian, German and Dutch SSKs operating alongside British SSNs.
10 boats is about the minimum needed to sustain a production drumbeat. SSN-AUKUS must fill a gap between 2027 and 2055 (Dreadnought’s replacement will take about 8 years to construct), and therefore, assuming a decade for the first SSN-A, delivery begins in 2038, with one boat delivered every two years. Any longer, and you run the risk of losing the drumbeat. Go faster, and you need to order more submarines.
Meanwhile, coastal anti-submarine warfare, and infrastructure security work, could be conducted by a uncrewed submarines. These are cheaper, lighter, wouldn’t infringe upon the manned submarine production industry, but are well-suited to local patrol and delousing.
SSN are expensive, but unless you cut all your nuclear submarine capability (not viable for the UK), mixed fleets will continue to present weird challenges. I don’t think any established or upcoming nuclear submarine power of comparable size to the UK currently operates a mixed fleet. France produces SSKs, but does not operate them themselves. Australia intendeds to switch to an entirely nuclear fleet. Brazil will likely phase out its SSKs once it has an SSN production line.
South Korea may retain their SSKs, but things may have changed by 2035.
Only Russia and China operate mixed fleets (India has no domestic nuclear attack submarines). Those three nations are on a different scale to the UK.
A mixed fleet isn’t too much of problem if many parts and prcoedures are common. In fact when using turbo-electric propulsion on SSNs. The only difference between an SSN and SSK is the main & auxiliary power plant setup, maybe de-salination plant. Almost everything else from mess hall fixtures, through plumbing and torpedo tubes to sensors and combat systems can be the same or almost the same. We have a high-low mix of frigates, why not subs too.
They’re expensive for what they offer, they take up valuable construction area, they’d require design funding, they’re less flexible, and cutting the amount of SSNs damages the maintenance and sustainment of the fleet long after construction has ceased. They need a separate maintenance and training pipeline, and they’re slow.
The UK can build a limited amount of submarines. Nuclear submarine design and construction is a specialised skill. Rather than building two small, expensive runs of different submarine classes, or worse, building a small SSN run and buying in foreign SSKs, the UK should build a middling number of a single design (10-12) and focus all maintenance and sustainment on that class.
If the RN really needs a constabulary, coastal-ASW platform, procure a small fleet of uncrewed submarines.