Head-of-class Royal Navy (RN) nuclear-powered ballistic missile submarine (SSBN) HMS Vanguard returned to port at His Majesty’s Naval Base (HMNB) Clyde on 18 April 2026, having been on patrol for a record 205 days at sea.

On the face of it, this would appear a triumph; joining the HMS Vanguard crew in the final part of their homeward journey was UK Prime Minister Sir Keir Starmer, UK Defence Secretary John Healey, First Sea Lord General Sir Gwyn Jenkins and UK Chief of Defence Nuclear Madeline McTernan.

In fact, the record-breaking deployment of HMS Vanguard is a symptom of the RN’s chronic shortage of submarine availability.

There are four SSBNs in the Vanguard class, one of which is always at sea performing the RN’s nuclear continuous at sea deterrent (CASD) mission. The other SSBNs would typically be in refit/maintenance, with one of them, having ideally completed that process, being prepared for deployment.

The Vanguard class was originally designed to conduct normal patrols of two months, extended patrols of three months (12 weeks) or a maximum duration at sea of up to four months. Given the boats’ nuclear propulsion, as long as all systems continue to function correctly the only limiting factor to patrol duration is storage space for the crew’s food (which can in theory be mitigated by replenishment at sea at the risk of giving away the SSBN’s position).

However, a lack of SSBN availability has seen more than just the latest Vanguard-class patrol breaking records by exceeding 200 days.

Just prior to the return of HMS Vanguard, another Vanguard-class SSBN was deployed as a replacement for the CASD mission. However, the sighting by observers of a French Navy Suffren-class nuclear-powered attack submarine (SSN) inbound to HMNB Clyde on 20 April appeared to confirm that the French boat had been used to escort HMS Vanguard’s replacement out to sea, indicating the lack of availability of any RN Astute-class SSN to perform the task.

When any RN SSBN puts to sea on a CASD deployment it is typically screened by a variety of assets, including an SSN and air patrols by Royal Air Force P-8 Poseidon maritime patrol aircraft, to clear the patrol area of potential threats, such as Russian submarines that might attempt to ‘tail’ it.

However, there are currently no available RN Astute-class SSNs to perform such duties. The current status of the RN’s seven-strong fleet of Astute-class SSNs is believed by Warsight to be as follows: HMS Anson is currently deployed to the Middle East, HMS Astute is at HMNB Devonport for a two-year Mid-Life Re-Validation Period (MLRP), HMS Audacious is in the process of returning to service at HMNB Devonport after a period of extended maintenance, both HMS Ambush and HMS Artful are non-operational at HMNB Clyde, while HMS Agamemnon is currently conducting post-commissioning sea trials and HMS Achilles is still in build at the BAE Systems shipyard in Barrow-in-Furness.

When approached by Warsight with a view to verifying the above, an RN spokesperson at the UK Ministry of Defence declined to comment, citing sensitivities regarding the operations of RN submarines.

The official Royal Navy website proudly states, “We’re ready for the battles ahead.” They are clearly not: a reality that the First Sea Lord himself has conceded to the Swedish newspaper Svenska Dagbladet.

A solution that will take time

The lack of RN submarine availability is substantially down to a lack of shore-based submarine servicing infrastructure. In recent years multiple remedies for this situation have been initiated, but they will take time to bear fruition.

The main two locations where UK submarine support takes place are Faslane (HMNB Clyde) in Scotland, which typically conducts routine pre-deployment maintenance, and HMNB Devonport in Plymouth, southwestern England, which specialises in deep maintenance and service life extensions. However, as Navy Lookout reported in July 2025, “Priority for the shiplift in Faslane is always given to the Vanguard-class SSBNs” and “There is only one other dry dock available in Devonport for SSNs until the 10 Dock upgrade is completed in 2027.”

The Submarine Waterfront Infrastructure Future (SWIF) programme at Devonport, which will include a new non-tidal maintenance berth in 5 Basin as well as a refurbished 10 Dock at the base, was formally launched in December 2016, but the UK’s Submarine Delivery Agency (SDA) did not formally sign a SWIF contract, with Babcock International, until November 2023.

In late 2023, meanwhile, the UK MoD initiated the Additional Fleet Time Docking Capability (AFTDC) programme, known as Programme Euston, to provide two floating dry docks for RN SSN and SSBN maintenance at Faslane.

Floating dry docks are a convenient way to add maintenance capacity and can be relocated if necessary.

Currently in the concept phase, Programme Euston is unlikely to provide new floating dry docks at Faslane before the early 2030s.

More recently, on 15 January 2026, a 100-day Submarine Maintenance Recovery Plan (SMRP) was launched to tackle the RN’s chronic submarine maintenance delays. The SMRP is intended to unify previously fragmented initiatives across the UK submarine enterprise to improve the pace and predictability of maintenance delivery and thus return more RN boats to active service more quickly.

Lord Robertson’s words ring true

The lack of RN submarine availability inevitably adds weight to the already solemn words of Baron Robertson of Port Ellen: the 10th NATO secretary general and a former UK defence secretary who warned on 14 April 2026 that the UK government is suffering from “a corrosive complacency” in not adequately preparing its armed forces for conflict.

The UK government was stated to be facing an estimated GBP 28 billion (EUR 32.3 billion) shortfall in defence funding even before the US/Israeli conflict with Iran sending energy prices soaring and exacerbated Whitehall’s budgeting headaches. Maintaining a nuclear deterrent along with two fleets of nuclear-powered submarines – along with plans to replace the RN’s current SSNs and SSBNs with the SSN-AUKUS and Dreadnought classes respectively – does nothing to alleviate that dilemma.