Missile M51

The M51 is a French submarine-launched ballistic missile developed to succeed the M45 aboard the ballistic missile submarines of the Force océanique stratégique. It descends from the M5 programme begun by Aérospatiale in the late 1980s, a design planned to reach some 11,000 km with ten new-generation warheads. In 1996 the programme was restructured, cutting development costs by about 20%, and renamed M51. Its three-stage solid-propellant motors derive their technology from the solid boosters of the Ariane 5 space launcher. ArianeGroup and its predecessors have been industrial prime contractor since 2000, covering design, production, in-service support and end-of-life dismantling. Development cost roughly €5 billion; in December 2004 a serial production order worth about €3 billion was placed, covering ten years of output.

The M51 measures about 12 m in length and 2.3 m in diameter, with a launch weight of more than 50 tonnes, usually given as about 52 tonnes. Its three solid-propellant stages sit beneath a nose section fitted with an extensible aerospike, deployed after launch to reduce aerodynamic drag. Guidance is astro-inertial. The payload bus carries multiple independently targetable re-entry vehicles (MIRVs) together with penetration aids. On a full-range trajectory the missile climbs to an apogee above 2,000 km before its warheads re-enter the atmosphere at around Mach 20; a top speed of Mach 25 is often quoted. The operational range is classified and is usually estimated at 8,000 to 10,000 km.

The first version, the M51.1, entered service in 2010 aboard Le Terrible. It carried the TN 75 thermonuclear warheads inherited from the M45, reportedly up to six per missile, although some sources cite up to ten MIRVs, with penetration aids. The M51.2 followed, paired with the new tête nucléaire océanique (TNO) warhead that replaced the TN 75. Its first acceptance firing took place from Le Triomphant on 1 July 2016 and the version was deployed from that year; its range is reported to exceed 9,000 km.

The M51.3 is the current standard. Warhead work began at the CEA in 2013 and the DGA launched development of the missile in 2014; in May 2016 Airbus and Safran, later ArianeGroup, partnered on the programme. The version was designed to improve range, accuracy and penetration against missile defences, with a reported range of more than 9,500 km. It carries the TNO-2 warhead, reportedly four to six MIRVs of about 100 kt each. The first flight test took place on 18 November 2023 from the DGA missile test centre at Biscarrosse in the Landes: the unarmed missile came down in the North Atlantic several hundred kilometres from any coast, and the flight served as the qualification test. The Minister of the Armed Forces signed the operational commissioning on 24 October 2025, about ten years after the programme was launched, on schedule and on budget. The M51.3 equips all four Triomphant-class submarines, each carrying 16 missiles. Its first launch from a submarine came on 6 October 2026, when Le Vigilant, emerging from its mid-life major overhaul (IPER), fired an unarmed missile off Finistère in an acceptance firing conducted as Operation SMERTRIOS and tracked by the DGA and the trials ship Monge. It was the seventh submarine firing of the M51 family and the thirteenth M51 launch overall.

A further version, the M51.4, is already under contract: on 28 August 2025 the DGA awarded ArianeGroup its design and production, seeking further gains in range, precision and penetration. It is to arm both the Triomphant class and the future third-generation submarines (SNLE 3G).

The M51 first flew on 9 November 2006 from Biscarrosse, followed by land tests on 21 June 2007 and 13 November 2008. The first submarine launch took place on 27 January 2010 from Le Terrible in Audierne Bay, Brittany, the missile flying about 4,500 km in under 20 minutes; a further firing on 10 July 2010 validated operational launch from the Triomphant class. The first failure, after five successes, came on 5 May 2013 from the submerged Le Vigilant off Brittany. Later tests included a land launch on 30 September 2015, a firing from Le Téméraire on 12 June 2020, a land launch on 28 April 2021 and a firing from Le Terrible on 19 April 2023. Every flight has been conducted without nuclear warheads.

The M51 arms the four Triomphant-class SSBNs of the Force océanique stratégique (FOST): Le Triomphant, Le Téméraire, Le Vigilant and Le Terrible, based at Île Longue near Brest. It will also equip the third-generation SNLE 3G class due from the mid-2030s, with the M51.4 planned for both classes. Its closest counterpart is the US Navy's Trident II D5.