The M51.3 Submarine-Launched Ballistic Missile (SLBM), developed by Ariane Group, has entered service with France’s Strategic Oceanic Force (FOST), the branch of the French Navy responsible for the country’s sea-based nuclear deterrent.

The M51.3 will be deployed aboard the Navy’s 4 LE TRIOMPHANT-class nuclear ballistic missile submarines (SSBNs). With an estimated 290 nuclear warheads, France possesses the fourth-largest nuclear arsenal in the world, and is one of only 2 NATO nations - alongside the United Kingdom - to operate an independent nuclear deterrent, separate from the American nuclear umbrella.

The new SLBM is the third variant of the M51, a fifth-generation strategic ballistic missile first fielded in 2010, and will gradually replace the earlier M51.1 and M51.2 versions. The French General Directorate for Armaments (DGA), the Joint Staff, the French Navy, the Atomic Energy and Alternative Energies Commission (CEA), and Ariane Group have collaborated over the past decade on the design, development, and production of the M51.3. According to Vincent Pery, Director of Defense Programs at Ariane Group, “in today’s evolving geopolitical context, the deployment of the M51.3 helps ensure the continued credibility of France’s oceanic nuclear deterrent.” First tested in southwestern France in November 2023, the M51.3 underwent a series of qualification launches that validated its performance and compliance with nuclear safety and SSBN operational standards. Its operational entry into service this month, according to French Defence Minister Catherine Vautrin, “embodies a major ambition of the 2024–2030 Military Programming Law: to accelerate the modernization of our capabilities and ensure the long-term credibility of our deterrence, the sovereign pillar of our security.”

The M51.3 missile is equipped with an upgraded oceanic nuclear warheads derived from the TNO design (TNO-2), featuring greater range, improved accuracy, and enhanced penetration capabilities compared to France’s existing systems. The missile measures about 12 m in length, weighs over 50 t, and uses a three-stage solid-propellant propulsion system. Each FOST-operated SSBN can carry up to 16 M51 missiles. While the French Navy has not disclosed the exact range of the M51.3, it is estimated to be between 5,000 and 6,200 miles (8,000–10,000 km). Nevertheless, following the introduction of the M51.3, the French military and ArianeGroup are already working on the next iteration of the successful missile — the M51.4.

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