New nuclear sub design review finished ahead of schedule

The SSN-AUKUS Preliminary Design Review was conducted in June and concluded on 1 July, three months earlier than the September date it had been expected to meet, according to an answer given in Parliament.

Ben Obese-Jecty, the Conservative member for Huntingdon, asked for what reason the scheduled September 2026 Preliminary Design Review date for SSN-AUKUS was missed and what the new date was.

Luke Pollard, the Minister of State for Defence, said: “The SSN-AUKUS Preliminary Design Review was conducted in June 2026 and concluded on 1 July as part of the ongoing Detailed Design and Long Lead (D2L2) phase of the programme.”

A Preliminary Design Review on a submarine programme locks the overall configuration before detailed design work proceeds at scale, covering the hull form, the compartment arrangement, the propulsion and combat system integration and the weight and stability margins. Passing it allows long lead items to be ordered against a stable design, which matters on a programme where reactor components and large forgings have ordering lead times measured in years.

SSN-AUKUS is the replacement for the Astute class and the design Australia will also build, developed by BAE Systems at Barrow with Rolls-Royce providing the reactor plant and a trilateral arrangement governing the common elements. The boat is larger than Astute, carries vertical launch capacity and is intended to accommodate uncrewed systems alongside torpedoes and cruise missiles.

Detailed Design and Long Lead runs to 2028, and the programme is midway through it, with Pollard confirming in a separate answer the same day that the number of boats will be settled before the phase closes. Steel will be cut on the first British hull next year, a milestone this publication has covered as it approached.

Design reviews slipping to the right has been the pattern across large defence programmes for a generation, which is what prompted the question. Submarine design on this programme has run with a deliberately conservative schedule built around the Barrow drumbeat, and Dreadnought holds the priority on the same design and build resources.

Australia’s Osborne yard in South Australia will build to the same design, and the Australian Submarine Agency has its own review gates aligned to the British ones, so an early conclusion on the British side gives both partners margin before detailed design work peaks. Rolls-Royce in Derby is producing reactors for both classes from a doubled site.

Obese-Jecty’s question assumed a missed milestone and received a date that had already passed. The review closed on the first of July and the programme has been running on from it since.