While a submerged submarine may be all but impossible to see from the surface, there are still numerous ways to track and monitor the vessels, and "noise" is one of those.
A moving submarine produces noise that makes it easy in many instances to track its location, speed and in many cases even identify the type of craft. The noise of a submarine, which can be distinguished from the ocean's natural noises, can radiate from hull vibration, power plant equipment, propellers, and flow noise.
France's New Stealth Submarine Plan
Efforts have been made to reduce the noise that a submarine gives off, and France has announced it has launched a new program for its Navy's third-generation nuclear-powered ballistic missile submarines.
A total of four boats of the sous-marin nucléaire lanceur d'engin (SNLE) program will be produced, and the first is expected to be delivered beginning in 2035, with the three following to arrive on a schedule of one every five years. The submarines, which haven't received a name yet, will be built by the Naval Group and are also expected to remain in service until the 2090s.
The contracting authorities were reported to be the DGA procurement agency and the Alternative Energies and Atomic Energy Commission.
According to reports, the submarines will be slightly longer and heavier than the current Le Triomphant-class, which entered service in 1995. Notably, the new class of boats will also be far more silent.
"They will not make more noise than a school of shrimp," Armed Forces Minister Florence Parly was quoted as saying by DefenseNews.
A SNLE-3G (Third Generation) program officer for the Marine Nationale (French Navy) also told Naval News, "The submarine will be so quiet that its radiated noise may be less than the ambient noise in the ocean."
The new class of French submarines is thought to be utilizing some of the technology developed for the Suffren-class attack submarine, and that could include the X-form rudders and pumpjet propulsor.
In addition, to be quiet the SNLE submarines will be equipped with what H I Sutton of Naval News reported was the Thales' ALICIA (Analyse, Localisation, Identification, Classification Intégrées et Alertes), a holistic sensor suite, which could combine a wide range of sensors and a SYBOBS 3.0 data processing system. This could be capable of Ultra-Low Frequency (ULF) detection, which could allow the submarines to track and identify even the quietest adversaries.
Artificial intelligence (AI) could also be employed to help the crew identify contacts, reducing the pressure on the crew. Whether this system could tell a school of shrimp from another SNLE-3G boat isn't clear however.
So far a lot of effort has already gone into this new class of submarines' development. According to Armed Forces Minister Parly, who announced the launch of the program at DGA's hydrodynamic technologies center at Val-de-Reuil, work on the SNLE has been underway for more than a decade.
"Fifteen million hours have already been spent on development studies, and a further twenty million will be necessary for each submarine," she noted.
Making a submarine that is truly as quiet as the ocean doesn't come quickly.
Peter Suciu is a Michigan-based writer who has contributed to more than four dozen magazines, newspapers and websites. He regularly writes about military small arms, and is the author of several books on military headgear including A Gallery of Military Headdress, which is available on Amazon.com.