UK Confirms 2027 Steel Cut for First SSN-AUKUS Submarine and £15 Billion Warhead Investment

The United Kingdom government published its Defence Nuclear Enterprise 2026 Annual Update to Parliament on September 15, 2026, confirming that steel will be cut on the first UK SSN-AUKUS submarine in 2027 and setting out a £15bn investment in the warhead program alongside £6bn for submarine infrastructure at Barrow-in-Furness and Raynesway. Naval Technology reported the figures the same day.

"On current plans, steel will be cut on the first UK SSN-AUKUS submarine in 2027, marking the start of production," the report states. The program "remains focused on delivering the first Royal Navy SSN-AUKUS submarine into service in the late 2030s." Contracts worth about £4bn have already been placed, according to the update, supporting development of the capability and the industrial infrastructure needed for the next generation of attack submarines.

The size of the future fleet has not been fixed. Decisions on the total number of submarines to be procured "are expected to be taken before the end of the D2L2 phase in 2028," the report says, referring to the Detailed Design and Long Lead phase.

The stated objective is a continuous production cadence of one SSN-AUKUS submarine every 18 months, doubling the current build rate and enabling the parallel construction of SSN and SSBN classes. The modernization needed to reach that rate will entail an investment of approximately £6bn over the Spending Review period, the update says. UK boats will be built at BAE Systems' Barrow-in-Furness shipyard, with reactors supplied by Rolls-Royce at Raynesway. The Royal Australian Navy will also operate SSN-AUKUS submarines, built at Osborne Naval Shipyard in South Australia.

Both figures come from the Defence Investment Plan. The report describes the second as going "into infrastructure programmes in Barrow-in-Furness and Raynesway which will grow the capability of the enterprise to be able to produce a submarine every 18 months in the future."

On the ballistic-missile submarine side, the update reports that the Dreadnought class build program remains within the previous government estimate of £41bn, made up of £31bn plus £10bn contingency. Spend in the year to March 2026 was £3bn, bringing the total to £23.2bn. The program "continues to face significant pressures and associated risks given the complexity of this mega project and the wider economic environment," according to the report. HMS Dreadnought, the first of class, is due to complete sea trials and be ready to enter service in the early 2030s. Steel was cut on the fourth and final boat, HMS King George VI, at Barrow-in-Furness in September 2025, and an £8.4bn investment into the next stage of the build program was announced in July 2026. The boats will carry Trident II D5 missiles armed with sovereign UK nuclear warheads.

The Royal Navy's current attack submarine is the Astute class, first introduced in 2014 and equipped with Tomahawk cruise missiles and Spearfish torpedoes. HMS Agamemnon, the sixth boat of the class, was commissioned into the Royal Navy in September 2025.

GlobalMilitary.net's Royal Navy fleet inventory currently lists six Astute-class boats in service with one more on order, four Vanguard-class ballistic-missile submarines in service, and four Dreadnought-class boats on order. The UK nuclear forces page records a warhead inventory of 225.

The update also covers the legacy fleet. Since 1980, 23 nuclear-powered submarines have left service: 16, four of them defueled, are stored at Devonport Dockyard, and the remaining seven, all defueled, are at Rosyth Dockyard. On infrastructure, the concept design for SMITE2, a new submarine propulsion testing facility, was completed in early 2026, and remediation work at Ramsden Dock has advanced.

The next milestones are the 2027 steel cut at Barrow-in-Furness, which the report says will mark the start of SSN-AUKUS production, and the decision on the number of boats expected before the end of the D2L2 phase in 2028. The first Royal Navy SSN-AUKUS submarine is planned to enter service in the late 2030s, with HMS Dreadnought due to precede it in the early 2030s.