Fourth New French Nuclear-Powered Submarine Starts Sea Trials

Sea trials begin for the De Grasse nuclear attack submarine as it is guided out of Port Militaire in Cherbourg.
Sea trials begin for the De Grasse nuclear attack submarine as it is guided out of Port Militaire in Cherbourg. Image: French Navy
02/03/2026

The French Navy’s fourth Suffren-class nuclear attack submarine (SSN) De Grasse has begun her sea trials.

The 99-metre boat, which displaces 5,200 tonnes fully submerged, has sailed out of Port Militaire in Cherbourg, as per a recent statement by the Marine Nationale. She is headed initially for the English Channel and then on into the Atlantic.

The sea trials, intended to validate the boat’s technical and operational capabilities, will be carried out by French Navy submariners under the supervision of experts from the French Defence Procurement Agency (DGA), Naval Group, and TechnicAtome. 

Assuming successful completion, they will allow the boat to meet its scheduled delivery date later in 2026. 

The first three SSNs have already been commissioned into active service: the first-in-class, Suffren in June 2022, Duguay-Trouin in April 2024 and Tourville in July last year.

The final two submarines in the programme, Rubis and Casabianca, are currently under construction and are also due to be delivered before the end of the decade. 

The boats are armed with MBDA naval cruise missiles and SM39 Exocet anti-ship missiles, as well as F21 heavyweight torpedoes produced by Naval Group.

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