Le Triomphant-class (SNLE-NG)

The Triomphant class comprises four nuclear-powered ballistic missile submarines (SSBN) of the French Navy, designated SNLE-NG. It is the second generation of French SSBNs, succeeding the six Le Redoutable-class boats that served from 1971 to 2008, and forms the sea-based component of French nuclear deterrence, the Force océanique stratégique (FOST). The programme was decided by a defence council chaired by President François Mitterrand in autumn 1981, with requirements for about one-thousandth of the radiated noise of the Le Redoutable class, sonar ten times more sensitive, deeper diving and larger missile tubes for a future heavier missile. Six boats were initially planned; the order was cut to four after the end of the Cold War.

The boats were built by DCN at Cherbourg in the Laubeuf assembly hall, opened in 1989. Each hull was assembled from five fully outfitted sections (propulsion, electrical, reactor, missile compartment and operational spaces) joined afterwards. Le Triomphant was laid down in October 1986, floated out in November 1993 and declared operational in March 1997; Le Téméraire followed in 1999, Le Vigilant in 2004 and Le Terrible in September 2010. The submarines are 138 m long, 12.5 m in beam and 10.6 m in draught, and displace 12,640 t surfaced and 14,335 t submerged. The pressure hull is made of a high-yield steel designated 100 HLES, with a test depth over 400 m.

A K15 pressurised water reactor of 150 MWth, developed by Technicatome, delivers 30.5 MW (about 41,500 hp) to a single shaft. The class was the first French submarine class with a pump-jet propulsor; emergency propulsion relies on batteries and two SEMT Pielstick diesel-alternators. Submerged speed exceeds 25 knots. Quieting measures include flexible piping, auxiliaries on elastic mounts and decks isolated from the hull. The sensors comprise bow and large flank sonar arrays and a VLF towed array, the DSUV 61B, about one kilometre long. Le Terrible introduced a new integrated combat system, SYCOBS, later shared with the Suffren-class attack submarines, and new Thales sonars. The crew numbers about 110, including 15 officers, and patrols last about 70 days.

Each submarine has 16 missile tubes. The first three boats entered service with the M45 missile, while Le Terrible was built for the M51 and made the first submarine launch of an M51 in January 2010. The first three boats were brought to Le Terrible's standard during their major refits (IPER) in the 2010s, at a cost of about €2 billion; the last M45 was offloaded in 2016. The M51.2, carrying the TNO (tête nucléaire océanique) warhead, was first fired on 1 July 2016 from Le Triomphant after its 2014–2016 refit. The M51.3 entered operational service in October 2025. On 6 October 2026 Le Vigilant made the first submarine launch of an M51.3, fired unarmed off Finistère as an acceptance firing after its refit; President Emmanuel Macron described it as a very important moment for France's strategic credibility. For self-defence, the boats have four 533 mm tubes for F21 heavyweight torpedoes and Exocet SM39 anti-ship missiles, 18 weapons in total.

The class is based at Île Longue, near Brest, in Brittany. France keeps at least one SSBN on patrol at all times, with a second at sea or ready to sail. In February 2009 Le Triomphant collided underwater with the Royal Navy SSBN HMS Vanguard in the Atlantic; its bow sonar dome was damaged and it returned to Brest under its own power. The class is to be replaced under the SNLE 3G programme: steel was cut on the first boat in March 2024, and on 2 March 2026 President Macron announced that the lead boat will be named L'Invincible, to be commissioned in 2036, with the following boats at roughly five-year intervals.