France’s Defense and Intervention Frigate stands apart from other modern naval vessels because of its sharply inverted bow. The distinctive design also delivers better performance at sea, according to Nicolas Guiraud, the former French Navy captain who commanded the first ship during trials.

Guiraud commanded the Amiral Ronarc’h for four years until July and now serves as a marketing director at Naval Group, which builds the frigate. He said the bow allows the ship to push through waves without the heavy impacts that produce slamming and vibration.

“Fewer vibrations mean a ship that ages much more slowly, cracks that won’t form, computer connectors that won’t disconnect,” Guiraud said during a Nov. 4 interview at the Euronaval maritime exhibition in Paris.

Reduced vibration also improves conditions for sailors aboard the vessel. Guiraud said crew comfort was not the primary reason for the design, but remained important because rested sailors are better positioned to make sound decisions.

French Navy Chief of Staff Adm. Christophe Cluzel told lawmakers last month that the FDI had answered criticism from competitors. He described the frigate as extremely maneuverable and stable, “contrary to what some comments may have suggested.”

Sweden announced in May that it plans to purchase four of the frigates, which are already used by the French and Hellenic navies. The French Navy received its first FDI in October 2025.

“This design, which at first raised questions and left many people dubious, is now convincing a lot of people,” Guiraud said. Naval Group also displayed an 8,000 ton drone carrier frigate concept with an inverted bow at Euronaval.

The inverted bow appeared during the 19th century and later returned on support vessels, but remained new territory for a modern frigate. Naval Group studied the concept for more than a decade beginning in the mid 2000s.

That work included extensive trials in towing tanks, hydrodynamic modeling and evaluations of radar signatures. Naval Group says the inverted bow produces a smaller radar profile than a conventional flared bow.

The United States Navy operates Zumwalt class stealth destroyers with inverted bows. Their tumblehome configuration narrows above the waterline, while the French frigate uses a flaring hull.

Guiraud’s command of the Amiral Ronarc’h included an extended deployment from the Arctic Circle to the Equator. He previously served aboard a French multirole FREMM frigate and other ships from earlier generations, where monitoring hull fatigue was “a central concern.”

Feedback from the FDI so far indicates that structural wear has not become an issue, according to Guiraud. He said the combination of the inverted bow, the ship’s length to width ratio and stabilizing fins means “this platform doesn’t vibrate, it doesn’t experience shocks. And so we believe it will age much better.”

The frigate uses a combined diesel and diesel propulsion system designed for efficient energy use. Although its advertised range is 5,000 nautical miles while traveling at 15 knots, Guiraud said the actual range is “a good 10% more.”

The vessel has a maximum speed of 27 knots and has maintained 20 knots during sea state 6 conditions. Such conditions feature very rough seas and waves measuring 4 to 6 meters, or 13 to 20 feet.

The Amiral Ronarc’h has encountered sea state 7, which can include waves reaching 9 meters. Guiraud recalled slowing slightly while taking waves directly from the front in sea state 6, then returning to 20 knots after changing course to place the waves slightly ahead of the beam, “without any particular concern for the integrity of our systems.”

The bow and stabilizing fins also allow the frigate to continue military operations in rough conditions. Guiraud said operating a helicopter or towed array sonar during sea state 5 presented “no problem at all,” while operations during sea state 6 depend on wavelength, swell and wind strength.

The FDI displaces 4,500 metric tons while providing the same military capabilities as a 6,000 ton frigate, according to Guiraud. He said smaller vessels generally face greater challenges because they move more, yet the Amiral Ronarc’h maintains the same standards.

Guiraud dismissed concerns that additional spray from the bow could threaten weapons. Spray rails divert water, and the equipment is designed to remain functional when wet.

“There are no waves sweeping across the foredeck. There’s only spray, and our equipment is designed to be waterproof enough to function despite that.”

The FDI’s bow also sits high enough that conditions capable of submerging the foredeck would force any vessel to change course. Guiraud said no ship can remain immune when a sufficiently large wave submerges its superstructure.