TOULON, France – The French Navy successfully completed a record-breaking saturation dive to 265 meters (869 feet) using an electronic rebreather, a feat achieved within a hyperbaric chamber at the CEPHISMER (Centre Expert Plongée Humaine et Intervention Sous la Mer) facility in Toulon, France, on February 10, 2026. The two-week experiment, dubbed “ENTEX 51,” involved three test divers and a military nurse living within a complex of interconnected modules.
The dive commenced on January 27, 2026, with divers descending into a “wet” caisson filled with 15°C (59°F) water. Their objective was to manipulate a mock-up submarine hatch, operating ventilation systems and securing attachments while breathing a helium-oxygen mixture under a pressure of 27.5 bars – equivalent to the pressure experienced at a depth of 265 meters. “Vanne 876 fermée!” (“Valve 876 closed!”), “Paré en pression!” (“Ready for pressure!”) and “1, 2, 3… Top, mise en pression!” (“1, 2, 3… Top, pressurization!”) were among the commands exchanged as the team prepared for the dive, according to observations during the initial stages of the operation.
ENTEX 51 builds upon the Navy’s previous experimental dive to 200 meters in 2025 (ENTEX 50). According to Captain of Frigate Arnaud Le Béguec, commander of CEPHISMER, the current experiment represents a new world record for the deepest saturation dive completed with an electronic rebreather. The CEPHISMER facility, established in 1945 as the Groupe de Recherches Sous-marines (GRS), has evolved through several iterations – including the GERS (Groupe d’Études et de Recherches Sous-marines), GISMER (Groupe d’Intervention Sous la MER), COMISMER (COMmandement de la plongée et de l’Intervention Sous la MER) – before becoming the current Centre Expert in 2023.
The experiment utilized three modules: a living area equipped with bunks, a washroom, and a kitchenette; a turret; and a water-filled tank. The divers and nurse remained enclosed within these modules throughout the 14-day period, under constant surveillance and control by CEPHISMER personnel. The program aims to push the boundaries of human underwater capabilities in a controlled manner, focusing on operational and technical advancements.
CEPHISMER functions through specialized divisions, including a risk management in diving pole, an innovation/future preparation pole, and the Groupe d’intervention sous la mer (GISMER), which handles underwater missions beyond standard human diving operations. The center also incorporates experts from the Army, National Gendarmerie, and the Health Service of the Armed Forces.
The Navy stated that ENTEX 51 is part of a long-term project to improve the mastery of human capabilities at depth, with objectives including the control of seabeds and the ability to rescue distressed submarines. The data collected during the dive will be used to validate procedures and concepts before being tested in a natural environment. The current commander of CEPHISMER is Captain of Frigate Arnaud Le Béguec, who assumed command on August 26, 2024, succeeding officers in a lineage tracing back to members of the original underwater research group, including Commander Philippe Tailliez.
