16,500-ton nuclear submarine to sustain France’s deterrence through 2090

Naval Group presented a scale model of France’s next-generation SNLE 3G nuclear-powered ballistic missile submarine at Euronaval 2026 in Paris. The four-submarine L’Invincible-class program will replace the existing Le Triomphant-class fleet between 2037 and 2052. France has maintained a continuous at-sea nuclear deterrent since 1972. The new submarines are intended to preserve this capability and carry the next generation of submarine-launched ballistic missiles. Each vessel will measure 482 to 492 feet (147 to 150 meters) and displace approximately 16,534 tons (15,000 tonnes) when submerged. By comparison, the Le Triomphant-class submarines measure 453 feet (138 meters) and displace approximately 14,335 tons.

The lead vessel, L’Invincible, is scheduled for launch in 2036 and delivery in late 2037. President Emmanuel Macron announced its name on March 2, 2026, at the Île Longue submarine base. Each submarine will use a 220 MW K22 pressurized-water reactor developed by TechnicAtome, alongside pump-jet propulsion and X-shaped stern control surfaces. The reactor has a thermal rating of approximately 220 MW, compared with 150 MW for the K15 reactor used in the Le Triomphant class. This represents a 46.7 percent increase in thermal power, although it does not translate directly into an equivalent increase in propulsion power. The K22 modular reactor assembly is planned for 2028 and is also associated with France’s future France Libre aircraft carrier program

New sonar systems and missile capabilities

Thales is developing the ALICIA sonar architecture, combining a new bow sonar, passive flank arrays and the ALRO optical-technology towed sonar. ALRO will deploy between the upper X-shaped stern control surfaces. The SYCOBS 3.0 processing system is designed to handle ten times the acoustic data volume of current French ballistic missile submarines.

Artificial intelligence will assist with contact identification, classification and simultaneous tracking. Acoustic insulation, specialized coatings and magnetic-signature reduction are also intended to make the submarines harder to detect. Each vessel will retain 16 launch tubes for M51 submarine-launched ballistic missiles. The M51.4 variant is expected in the mid-2030s. Four 533 mm torpedo tubes will accommodate F21 heavyweight torpedoes. The crew will comprise approximately 100 to 110 personnel, with patrols lasting nine to ten weeks.

Construction schedule and industrial partners

The SNLE 3G program entered full-scale development in February 2021. Naval Group cut the first hull steel at its Cherbourg shipyard on March 20, 2024. A November 2025 contract covered detailed design, equipment procurement and construction of L’Invincible. The first submarine is scheduled for delivery in late 2037, followed by the remaining vessels in 2042, 2047 and 2052. The submarines will retain a 39-foot (12.5-meter) beam, close to that of the Le Triomphant class, limiting modifications at Île Longue. Their greater length and displacement will provide additional space for machinery, acoustic insulation and future upgrades rather than extra missile tubes.

ArianeGroup is developing the M51.4 missile under a contract awarded by France’s Directorate General of Armaments (DGA) on August 28, 2025, Safran Electronics & Defense is developing the CI4 inertial guidance unit. Around 500 French companies are expected to contribute to the program, supporting approximately 3,000 skilled direct jobs and involving nearly one million components. The industrial effort is estimated at 20 million working hours, with French companies accounting for 90 percent of the program’s total added value. Naval Group, TechnicAtome, Thales, ArianeGroup and Safran are among the main industrial partners. France must introduce the four new submarines while keeping at least one vessel continuously on patrol. Delays in construction, reactor qualification, missile integration or testing could place additional pressure on the aging Le Triomphant fleet. The new submarines are expected to preserve France’s sea-based second-strike capability through 2090.

Source: https://interestingengineering.com/military/france-nuclear-submarine-program-deterrence