Rubis-class submarine

The Rubis class is a class of nuclear-powered attack submarines operated by the French Navy. It originally comprised six boats, the first entering service in 1983 and the last in 1993. Two additional units originally planned were cancelled as a result of post-Cold War budget cuts. All submarines of the Rubis class have been based at Toulon and are part of the Escadrille de sous-marins nucléaires d'attaque. Smaller than contemporary designs of other major world navies, the Rubis class shares many of its system designs with the conventionally-powered Agosta class. In the late 1980s, the Rubis class was proposed to Canada in the context of their plan to acquire nuclear-powered submarines.

The submarines of the class were built in two batches, with the final two built to an improved standard to reduce noise emissions that plagued the original design. Dubbed the AMÉTHYSTE rebuild, the first four hulls were refitted to its standard until they were practically indistinguishable from the final two hulls.

The Rubis class is being phased out and replaced with a new generation of nuclear-powered attack submarines, the Suffren class. The lead boat, Suffren, entered operational service in June 2022. Four of the six Rubis-class submarines, Saphir, Rubis, Casabianca and Émeraude have been decommissioned in 2019, 2022, 2023 and 2024 respectively.

The Rubis class was the second attempt at constructing a nuclear-powered attack submarine. The first, also dubbed Rubis, had been authorised in 1964 but cancelled in 1968, just as the first boat was about to commence construction. However, a new naval plan in 1972, called Plan Bleu, stated a requirement for 20 attack submarines of both nuclear-powered and conventionally-powered types. The new design, designated Type SNA 72 and called a sous-marin nucléaire de chasse (French: nuclear attack submarine) was smaller than any contemporary nuclear-powered attack submarine design in other major world navies. The small hull design was capable due the development of a compact, integrated nuclear reactor-exchanger with turbo-electric drives. Even then, the project was only considered feasible if equipped with weapons and sensors already in service, with the fire-control, torpedo-launching and submarine-detection systems also found in the Agosta class.

As built the first four submarines of the class measured 72.1 metres (236 ft 7 in) long overall with a beam of 7.6 m (24 ft 11 in) and a draught of 6.4 m (21 ft 0 in). The Rubis class had a standard displacement of 2,265 tonnes (2,229 long tons), 2,385 t (2,347 long tons) surfaced and 2,670 t (2,630 long tons) submerged. The boats are of single-hull construction made of 80 HLES high elasticity steel and the forward diving planes are situated high on the conning tower. The Rubis class can dive to depths over 300 m (980 ft).

The submarines are powered by a CAS-48 pressurised water nuclear reactor creating 48 megawatts utilising 7% low-enriched uranium, driving two 3,950-kilowatt turbo-alternator sets. These power a single propeller creating 7,100 kW (9,500 shp). At low speeds, the submarines use natural circulation to reduce noise emissions. In case of a reactor failure, the Rubises have an emergency electric motor powered by batteries or a SEMT-Pielstick 16PA4 diesel generator set with an output of 480 kW (640 hp; 650 PS). On battery power, the vessel has a range of 50 nautical miles (93 km; 58 mi) and endurance for 15 hours. The submarines had a cruising^{[citation needed]} speed of 25 knots (46 km/h; 29 mph) and endurance of 45 days (60 days maximum). Manned by two (alternating) crews, they have an active yearly service of 240 days. The crew initially^{[clarification needed]} numbered 66, including 9 officers.

Sharing sensors and weapons with the Agosta class, the Rubises have four 533-millimetre (21 in) torpedo tubes forward. They have stowage for a mix of 14 F17 Mod 2 torpedoes and SM39 Exocet anti-ship missiles. The submarines can fire and guide two torpedoes simultaneously. Instead of torpedoes, the submarine can embark^{[clarification needed]} FG 29 mines. The submarines was initially fitted with a DRUA 33 navigation/search radar, ARUR and ARUD electronic warfare systems, DSUV 22 multi-function passive sonar array, DUUA 2B active sonar, and DUUX 2 acoustic intercept sonar.

The initial design of Rubis proved to be problematic with unexpectedly high noise levels. This led to the Améthyste silencing program (AMÉlioration Tactique HYdrodynamique Silence Transmission Ecoute, literally Silent Acoustic Transmission Tactical Hydrodynamic Improvement) which was applied during construction of the fifth (Améthyste) and sixth (Perle) hulls. The hull form was reshaped and lengthened to 73.6 m (241 ft 6 in) while the superstructure and external bow were made of glass-reinforced plastic. To further reduce noise emissions, the machinery was given flexible mountings. The program included upgrades to the sonar and additional upgrades of the electronics. The Rubis class had a DSUB 62C towed passive sonar array, DUUG 2 sonar intercept, DMUX 20 sonar suite installed and had their acoustic intercept upgraded to DUUX 5. With the upgrades tested and proven, the original four boats were rebuilt to the same standards between 1989 and 1995 and were nearly identical to the final two ships of the class.