French Navy begins sea trials of De Grasse nuclear attack submarine before delivery in 2026.

On February 25, 2026, the French Navy announced that the nuclear-powered attack submarine De Grasse began sea trials following its first sortie from Cherbourg.

On February 25, 2026, the French Navy announced that the nuclear-powered attack submarine, the De Grasse, began its sea trials following a first sortie from Cherbourg on February 24, 2026. The trials mark the next phase of the Barracuda program to replace the Rubis-class submarines as part of a renewal plan extending to 2030. Delivery of this fourth Suffren-class submarine to the French Navy is scheduled for 2026.
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The Suffren-class is the second generation of French nuclear-powered attack submarines, replacing the Rubis class, with six boats planned and service entry stretching from 2022 to 2030. (Picture source: French Navy)

The transition to sea trials followed completion work and a sequence of dockside tests carried out in Cherbourg after the Suffren-class submarine’s transfer in May 2025 from Naval Group’s construction hall to the launch system and its float-out into the Cachin basin. The nuclear reactor achieved first criticality on December 12, 2025, during the procedure known as first divergence, and a ceremony for the formation of the blue crew took place on October 10, 2025, in Cherbourg. Sea trials will continue through 2026 under the French Defence Procurement Agency, in cooperation with the Atomic Energy Commission, Naval Group, TechnicAtome, and crews from the French Navy, with delivery scheduled in the same year to support the renewal of the French Navy’s nuclear-powered attack submarine force by 2030.

The submarine's namesake, François Joseph Paul de Grasse, was born on September 13, 1722, at Le Bar-sur-Loup in the then-Kingdom of France and died on January 11, 1788, at the Château de Tilly. A career officer of the French Royal Navy, he rose to the rank of Vice Admiral and played a central role during the American War of Independence. In 1781, he commanded the main French fleet in the Atlantic and secured control of the Chesapeake Bay on September 5, preventing British naval reinforcement of General Cornwallis and contributing directly to the Franco-American victory at Yorktown on October 19, 1781. The following year, on April 12, 1782, he was defeated and captured by the Royal Navy at the Battle of the Saintes in the Caribbean, an engagement that led to controversy and a court-martial after his release. Despite that setback, his action in the Chesapeake campaign remained decisive in the outcome of the war.

De Grasse, pennant number S638, is the fourth of six Suffren-class submarines ordered under the Barracuda program to replace the Rubis-class vessels that entered service from the 1980s. The first three units, Suffren, Duguay-Trouin, and Tourville, entered active service in June 2022, April 2024, and July 2025, respectively, while the fifth and sixth units, Rubis and Casabianca, remain under construction with planned deliveries before 2030. Construction of De Grasse advanced with the start of assembly on July 31, 2023, shortly after Tourville left the construction hall. During the sea trial phase, the submarine remains the property of Naval Group and TechnicAtome, while the French Navy exercises command at sea as delegated operator of the military nuclear system and retains operational control. The Defence Procurement Agency and the Atomic Energy Commission act as contracting authorities responsible for the trial process until acceptance and delivery to the French Navy.

The submarine measures 99.5 meters in length, 8.8 meters in beam, 7.3 meters in draft, and 8.4 meters in air draft, with a displacement of 4,650 t surfaced and 5,300 t submerged. It is constructed in steel at Naval Group’s Cherbourg-Octeville shipyard and operates with a crew of 65 sailors, reflecting a high degree of automation. Propulsion is provided by a TechnicAtome K15 pressurized water reactor rated at 150 MW thermal power, coupled to turbo-alternators delivering electrical power and supported by two emergency diesel engines rated at 480 kW. The propulsion chain drives a pump-jet system, and maximum submerged speed exceeds 23 knots, with a surface speed of 14 knots. Operational range is unlimited due to nuclear propulsion, with endurance constrained by 70 days of provisions.

The combat system integrates the SYCOBS combat management system, Thales UMS-3000 hull and flank sonar arrays, Thales Partner communications, and associated electronic support and navigation sensors. Armament is deployed through four 533 mm torpedo tubes with capacity for 24 weapons, including F21 heavyweight wire-guided torpedoes, SM39 Exocet anti-ship missiles, and MdCN naval cruise missiles capable of striking land targets at distances up to 1,000 kilometers. The Suffren-class also supports mine laying and incorporates countermeasure systems for torpedo defense. Facilities allow embarkation of combat swimmers and special forces, with provision for additional equipment to support insertion and extraction missions. These capabilities expand mission scope beyond anti-submarine and anti-surface warfare to include land-attack and special operations roles.

Nuclear-powered attack submarines, or SSNs, are distinct from ballistic-missile submarines in mission focus, concentrating on protection of strategic submarines, intelligence collection, escort of carrier or amphibious groups, anti-submarine warfare, anti-surface warfare, and strike missions. The first nuclear-powered attack submarine was the USS Nautilus, which entered service in 1955, initiating a transition toward long-endurance submerged operations. Nuclear propulsion eliminates the requirement for atmospheric oxygen, enabling sustained submerged deployment measured in months and sustained high underwater speeds without battery constraints typical of diesel-electric submarines. Conventional attack submarines must surface or snorkel periodically to recharge batteries, increasing detectability, while nuclear-powered units maintain continuous submerged operation. However, the main constraints of nuclear propulsion relate to technological complexity, cost, infrastructure requirements, and policies governing port access and decommissioning.

Several navies currently operate nuclear-powered attack submarines, including the United States, Russia, France, India, China, and the United Kingdom. The U.S. Navy transitioned to an all-nuclear attack submarine fleet by 1990 after decommissioning USS Blueback, and fielded classes such as Los Angeles, Seawolf, and Virginia, with ongoing development of a future SSN(X) design. The United Kingdom introduced HMS Dreadnought in 1963 and currently operates the Astute class while planning further nuclear-powered submarines under the SSN-AUKUS program. Russia inherited a large Soviet-built fleet and operates classes including Akula and Yasen, with multiple generations developed since the late 1950s. China operates Type 091 and Type 093 submarines with Type 095 planned, while India has leased Akula-class submarines and is developing indigenous nuclear submarine programs; Australia announced on September 15, 2021, its intent to acquire nuclear-powered submarines under the AUKUS framework, and Brazil continues development of its Álvaro Alberto nuclear submarine with construction approved on November 25, 2021.

The Suffren-class, developed under the Barracuda program launched in 2006, constitutes France’s second generation of nuclear-powered attack submarines and succeeds the Rubis class. Each boat has a submerged displacement of 5,300 t, length of 99.5 meters, and beam of 8.8 meters, making it larger than the 2,670 t Rubis class and enabling carriage of 24 weapons compared with 14 on its predecessor. The class incorporates a hybrid propulsion arrangement combining steam-driven turbines and electrical drive modes to balance speed and acoustic discretion, with a maximum submerged speed exceeding 25 knots and diving depth exceeding 350 meters. Crew complement is 63 to 65 personnel, depending on configuration, with dual crews assigned to each submarine to increase operational availability. Missions include protection of strategic ballistic-missile submarines, escort of naval task groups, intelligence gathering, special forces deployment, anti-submarine and anti-surface warfare, and precision land strike using cruise missiles, ensuring continuity of France’s nuclear-powered attack submarine capability through 2030 and beyond.

Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Ukraine, Russia, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.