France’s Third-Generation M51.3 Submarine-Launched Ballistic Missile Enters Service.

France has formally declared the third variant of its M51 submarine-launched ballistic missile, the M51.3, operational following a ministerial decision signed on October 24, 2025, and nuclear-safety validation in September 2025. The upgrade, fitted with the CEA TNO-2 oceanic warhead, increases range, accuracy and penetration, and primes a production ramp-up as serial deliveries begin.

The French Ministry of the Armed Forces announced on October 28, 2025, that France declared the M51.3 submarine-launched ballistic missile in operational service, following a decision signed on Friday, October 24, 2025, by Catherine Vautrin, French Minister for the Armed Forces and Veterans. ArianeGroup, prime contractor for the system on behalf of DGA, adds that the milestone caps a ten-year development effort delivered on schedule and within the initially defined budget and quality. The company confirms that nuclear-safety validation at Île Longue, French nuclear launcher submarines' base and aboard SSBNs concluded in September 2025, clearing the path for a production ramp-up ahead of embarkation. The ministry specifies that M51.3 carries the new oceanic nuclear warhead designated TNO-2.
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France fields the M51.3 SLBM on Triomphant-class subs, boosting range, accuracy, and penetration to reinforce its sea-based nuclear deterrent (Picture source: French Armed Forces).

“This milestone marks the culmination of ten years of development completed on schedule and within the initially defined budget and quality,” said Vincent Pery, ArianeGroup’s director of defense programs, who linked the decision to the recent award of the M51.4 follow-on contract. ArianeGroup notes that the qualification firing took place in November 2023 from the DGA’s Landes Ballistic Launch Base at Biscarrosse and that the entry-into-service process included two years of performance and nuclear-safety validation at Île Longue and at sea.

France’s procurement road to M51.3 stretches back two decades. After initial M51 development, the government placed a serial-production order with EADS Space Transportation in December 2004 under a fixed-price contract worth just over 3 billion euros, with support over ten years. Contemporary parliamentary reporting put the broader M51 program cost around 6.5 billion euros in January 2004 terms, a scale that underwrote the transition from the M45 to the larger-diameter M51 and an extensive test program. Early firings began in 2006, the first underwater launch from SSBN Le Terrible occurred on January 27, 2010, and a widely reported failure on May 5, 2013, forced a reset before a string of successful shots in 2015, 2016, 2020, 2021 and April 2023 set up the November 18, 2023 M51.3 qualification.

The M51 family remains a three-stage, solid-propellant system sized for the 16 launch tubes carried by each French SSBN. ArianeGroup describes the missile as approximately 12 meters long and over 50 metric tons, with an intercontinental reach that varies by payload. Official messaging around M51.3 highlights the triad of improvements over M51.2 that matter most for deterrence today: extended range, improved accuracy and enhanced penetration against modern missile defenses. In parallel, the ministry confirms adoption of CEA’s next-generation oceanic warhead TNO-2 for the new variant, while declining to discuss yield or loading, which remain classified.

The missile is still designed to be carried by French submarines. France’s four Triomphant-class SSBNs, based at Île Longue near Brest within the Strategic Oceanic Force, form the oceanic backbone of the deterrent with permanent at-sea patrols. Each boat fields 16 vertical launch tubes and will gradually transition to M51.3 as the system rolls out. The class will hand off in the mid-2030s to the third-generation SNLE 3G submarines, for which the first steel was cut at Cherbourg on March 20, 2024, and whose design from the outset accommodates successive M51 evolutions starting with M51.3 and continuing with M51.4 now under contract.

Recent test history explains the conservative, incremental upgrade path. France validates credibility with “operational conditions” firings from submerged SSBNs. Le Téméraire’s shot on June 12, 2020, and Le Terrible’s on April 19, 2023, bracket the M51.3 land-based qualification and demonstrate end-to-end chain integrity after the 2013 failure that followed five straight successes. The November 2023 qualification firing then closed the development loop ahead of nuclear-safety sign-off in September 2025 and the ministerial decision on October 24.

For French forces, M51.3 buys reach, maneuvering room and credibility. Added range enlarges the target set that can be held at risk from familiar Atlantic patrol boxes, reducing exposure while preserving assured second-strike. Accuracy gains and improved penetration complicate any adversary’s layered defenses, supporting a doctrine of strict sufficiency with a small arsenal. The ministry’s communiqué is explicit on these points and ties them to the evolving threat environment. With M51.4 development awarded in August and announced on September 7, 2025, Paris has ensured a continuous upgrade path through the arrival of SNLE 3G.

Written by Evan Lerouvillois, Defense Analyst, Army Recognition Group.

Evan studied International Relations, and quickly specialized in defense and security. He is particularly interested in the influence of the defense sector on global geopolitics, and analyzes how technological innovations in defense, arms export contracts, and military strategies influence the international geopolitical scene.