After completing fifteen years of operations, the Royal Navy’s nuclear-powered attack submarine HMS Astute will enter its Mid-Life Revalidation Period (MLRP). On June 30, the vessel arrived at the Devonport naval base, where it will be formally transferred to Babcock, the contractor responsible for executing the technical upgrade program. The goal of the MLRP is to extend the submarine’s operational life, incorporate improvements to its systems, and maintain its availability in line with the strategic scenarios projected for the coming years—following what was the longest-ever deployment by a Royal Navy submarine.
Commissioned in 2010, HMS Astute was the first of seven nuclear-powered submarines built by BAE Systems for the Royal Navy to replace the Trafalgar class. Unlike its predecessors, it is powered by a Core H-type reactor, which does not require nuclear refueling throughout its service life. However, its initial design did not prioritize long-term maintenance needs, and combined with limitations in shore-based infrastructure, this has restricted its operational availability and led to prolonged port stays.
The overhaul will be carried out primarily in Devonport’s dry dock number 14, where HMS Audacious has also been located since February 2025. Part of the preliminary work will take place while the submarine is still afloat, in line with procedures implemented by Babcock to optimize intervention times. Although the duration of the MLRP has not been officially disclosed, HMS Astute is expected to remain out of service for several years due to the complexity of the program. While all operational units of the class are assigned to the Faslane base in Scotland, Devonport remains the Royal Navy’s primary logistics and major maintenance hub for submarines.
Throughout its operational career, HMS Astute has played a key role in Royal Navy milestones, including being the first of its class to transit the Suez Canal and operate in Indo-Pacific waters during the 2021 carrier strike group deployment. It also took part in the early stages of Carrier Strike Group 2025 (CSG25) before returning to Plymouth. As a symbolic end to its first commission, the crew held a special sailing event off the coast of Devon for family members, friends, and guests—an unusual occurrence for this type of unit.
The Astute class currently comprises five submarines in active service: HMS Astute, HMS Ambush (2013), HMS Artful (2016), HMS Audacious (2020), and HMS Anson (2022). In October 2024, the sixth unit, HMS Agamemnon, was floated out, while the seventh and final submarine, HMS Achilles (formerly named Agincourt), remains under construction with completion expected by 2028.
The MLRP of HMS Astute is part of a broader effort to renew the UK’s undersea warfare capabilities. Alongside the conclusion of the Astute program, BAE Systems is advancing the construction of the new Dreadnought-class ballistic missile submarines, which will replace the current Vanguard-class vessels. In parallel, under the trilateral AUKUS agreement—linking the UK with Australia and the United States—the UK is actively involved in developing a new generation of attack submarines to succeed the Astute class. These initiatives are consolidating the transformation of the Royal Navy’s submarine fleet and reinforcing its role within the UK’s national defense and nuclear deterrence strategy.
*Image credits: Royal Navy
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