The M51 SLBM is a French submarine-launched ballistic missile, built by ArianeGroup, and deployed with the French Navy. Designed to replace the M45 SLBM (In French terminology the MSBS – Mer-Sol-Balistique-Stratégique "Sea-ground-Strategic ballistic"), it was first deployed in 2010.

Each missile carries six to ten independently targetable TN 75 thermonuclear warheads.

The three-stage engine of the M51 is directly derived from the solid propellant boosters of Ariane 5.^[6] Like other blunt-nosed SLBM examples, such as the Trident D5, the M51 uses an extensible aerospike in the nose.

The missiles are a compromise over the M5 SLBM design, which was to have a range of 11,000 km (6,800 mi) and carry ten new-generation tête nucléaire océanique' ("oceanic nuclear warhead") MIRVs.^[7] Design work on the M5 started in the late 1980s by Aérospatiale,^[8] before the programme was renamed the M51 in 1996, when development costs decreased by 20 percent.^[9] The M51 entered service in 2010.^[10]

After having spent €5 billion ($6.7 billion) developing the missile, the French government placed a €3 billion ($3.9 billion) order with EADS SPACE Transportation for the M51 in December 2004. The contract covered serial production of the M51 for 10 years, with the company to be responsible for sustained readiness support throughout the missile's life.^[11][12]

The M51 performed its first flight test (unarmed) on 9 November 2006 from the French missile flight test centre in Biscarrosse (Landes). The target was reached twenty minutes later, in the north-west of the Atlantic Ocean.^[13]

A second and third successful test were carried out on 21 June 2007^[14] and 13 November 2008.^[15]

On 27 January 2010, at 9h25, a missile was launched underwater by Le Terrible, from Audierne Bay off the coast of Brittany in north-western France.^[16] The missile reached its target 2,000 kilometres (1,100 nmi) off South Carolina; the 4,500-kilometre (2,400 nmi) flight took less than 20 minutes.^[17][18]

A 10 July 2010 test validated the Triomphant-class submarine's capacity to launch the M51 in operational conditions.^[19]

On 5 May 2013, an M51 flight test missile failed after being fired by a submerged ballistic missile submarine off the coast of Brittany. This was the first failed launch of the M51 after five successful launches since 2006.^[20]

In 2014 Airbus signed a deal with the French government for development work on an upgrade designated M51.3 to equip the SNLE 3G.

On 30 September 2015, an M51 was successfully test-flown from a land-based missile site near Biscarrosse to a desolate target in the North Atlantic.^[21]

On 10 May 2016 Airbus and Safran signed a joint 50-50 partnership to develop the M51.3 upgrade intended to enter service around 2025.^[22]

On 12 June 2020, a successful test launch of an M51.3 missile (supposedly) was conducted from the Le Téméraire Triomphant-class submarine off the south-west tip of Finistère (Brittany).^[23]

On April 28, 2021 French Ministry of Armed Forces announced that it had tested an M51 submarine-launched ballistic missile (SLBM). The test was not launched from a French Navy Triomphant-class submarine but from a land based facility located in South Western France.^[24]

On April 19, 2023 the French Ministry of Armed Forces announced another M51 test, launched from the French Navy Le Terrible SSBN.^[25]

M51.3 was test fired successfully in November 2023.^[26]

 France

• French Navy – Primary armament for the Triomphant-class SSBN and the future SNLE 3G SSBNs.

• M45 (missile)
• R-29 Vysota
• R-29RM Shtil
• R-29RMU Sineva
• R-29RMU2 Layner
• RSM-56 Bulava
• UGM-133 Trident II
• JL-2
• JL-3
• R-39 Rif
• R-39M