Rubis class submarine: The first nuclear attack submarine of the French Navy 

rubis class submarine

The Rubis class attack nuclear submarine is the smallest attack nuclear submarine in the world, with a submerged displacement of only about 2,700 tons. 

Although the smaller hull limits the weapon carrying capacity, power output, continuous navigation capability, and crew living space, it also enables the Rubis class submarine class to have better maneuverability and flexibility, making it suitable for sailing in the Mediterranean Sea with complex hydrology.

Submarines are difficult to be found because they have been sneaking under the sea for a long time, so they are a relatively large risk factor in naval battles. Since the enemy is also trying to find the submarine first during the engagement, the submarine must always be careful not to reveal its position. 

Diesel-propelled submarines, which were active during World War II, are virtually silent when powered by rechargeable batteries and run quietly by electric motors, making them ideal for covert operations. 

However, when the charge of the rechargeable battery is exhausted, it must be recharged by a diesel engine, so an external air supply is required. At this time, if the exhaust gas is discharged outside, it is easy to be attacked because it may leave traces and be discovered by the enemy.

USS Nautilus

For this reason, the navies of various countries are calculating a new power source that can sail infinitely in the sea without using diesel engines, and nuclear-powered submarines were born. 

Deployed in September 1955, USS Nautilus (SSN-571) was the first nuclear-powered submarine to operate underwater without needing oxygen. 

The “Nautilus” is equipped with a small nuclear reactor that can run for decades and supply oxygen by electrolyzing seawater using electricity from generators. Therefore, a nuclear-powered submarine can obtain unlimited energy, so its advantage is that it can be hidden under the sea surface during the entire operation period, and it does not need to surface as long as the crew has food to eat.

Despite the high cost of developing and manufacturing nuclear reactors, navies around the world rushed to acquire nuclear-powered submarines as soon as they became available in the mid-1950s.

As France pursued nuclear armament, strategic nuclear submarines were developed ahead of attack submarines, and France’s first nuclear-powered submarine, the Redoutable, was built.

 After World War II, France attempted to rebuild its military and ensure that its submarine fleet did not lag behind Britain’s. In the 1950s, the French Navy launched its own nuclear-powered attack submarine (SSN) program. 

When Charles de Gaulle took office as French President in June 1958, he announced that he would independently promote the expansion of strategic weapons along the military route. The French Navy devotes all its resources to supporting three-axis strategic weapons (strategic missiles, strategic submarines, and strategic bombers), prioritizing the development of nuclear-powered strategic submarines equipped with ballistic missiles.

In this way, the French Navy’s first attack submarine project received a budget to start construction in 1958, but it was stopped in 1959, the following year. The original order was first to secure an attack nuclear submarine and then accumulate practical experience to develop a strategic nuclear submarine. 

However, the order was changed because the de Gaulle government was eager to secure a three-axis strategic weapon. However, a strategic submarine equipped with ballistic missiles inevitably requires a huge hull. Spend much energy and time accumulating experience and skills in driving submarines.

Rubis class submarine: The first nuclear attack submarine of the French Navy 
Sapphire (S602), the second ship of the Rubis class submarine-class attack submarine, sailing at low speed near the Toulon naval base

The French Navy believes that it will be difficult to develop a new attack submarine due to the imminent need to replace the aging diesel-engined attack submarines and the lack of budget.

Therefore, the Rubis-class attack submarine project was launched in 1974. The hull and combat system were unchanged using the existing Agosta-class diesel-electric attack submarine (submerged displacement of 2,000 tons), and only the propulsion engine was changed to nuclear power. 

The Rubis-class submarine was the first attack submarine of the French Navy after World War II. After several twists and turns, it was finally successfully deployed.

Rubis class submarine: The first nuclear attack submarine of the French Navy 
Bridge view of the second Rubis-class ship, Safir (S602)

The Rubis-class attack submarine developed based on the existing diesel attack submarine has an underwater displacement of 2,700 tons, which is only about two-thirds of the underwater displacement of the Nautilus (4,092 tons). 

It is the smallest attack submarine currently in service in France. Suppose a nuclear propulsion engine is installed inside the submarine. In that case, a separate closed area is required for safety management, which greatly reduces the space inside the ship, so most nuclear-powered submarines solve this problem by enlarging the hull. 

In the case of Rubis-class submarines, the nuclear propulsion engines are installed in a limited small hull, so the space inside the ship is relatively small. Unlike the U.S. Navy’s attack submarines, which can operate for about four to six months, the French Navy’s Rubis-class attack submarines can only operate for an average of 45 days and a maximum of 60 days. 

In this case, the overall efficiency is lower because several submarines are needed to ensure sufficient combat time.

Rubis class submarine: The first nuclear attack submarine of the French Navy 
The third Rubis class

Using the existing Agosta-class hull, the Rubis-class attack submarine was built relatively quickly, and the engines themselves were developed using existing diesel-electric propulsion. 

Generally speaking, nuclear-powered submarines use the power generated by the nuclear reactor to run the boiler and use the high-pressure steam generated at this time to turn the turbine to propel it. However, the Rubis-class attack submarine uses nuclear turbine electric propulsion that takes full advantage of the existing hull.

Rubis class submarine: The first nuclear attack submarine of the French Navy 
Rubis-class attack submarine uses nuclear turbine electric propulsion.

In this method, the high-pressure steam generated by running the nuclear power boiler rotates the generator to generate electricity. The unique nuclear turbine electric propulsion method of the French Navy has the advantage of low navigation noise, but due to the complexity, bulkiness, and unreliability of the propulsion engine, other The national Navy did not adopt it.

Rubis class submarine: The first nuclear attack submarine of the French Navy 
HMS Amethyst, the fifth Rubis-class ship, moored at the Royal Navy’s Portsmouth Naval Base

The lead ship of the Rubis-class submarine (S601) carried only heavy torpedoes and installed four heavy torpedo tubes on the bow. The second ship, Saphir (S602), was upgraded to carry SM39 Exocet surface-to-ship missiles, Exocet SSMs fired from heavy torpedo tubes. Rubis’s main ship was later refitted for the same purpose.

Originally, the Rubis-class submarine inherited the flat-bow spherical hull because it used the hull of the Agosta-class submarine that appeared earlier. Diesel submarines often sail on the water. This hull type is more practical for ships that only sail in the sea. 

For nuclear-powered submarines, its disadvantage is high resistance. Therefore, most nuclear-powered submarines have drop-shaped hulls, and Rubis later changed the hull to a drop-shaped hull that is more suitable for underwater navigation.

The French Navy maintained a mobile carrier fleet of one or two ships and two submarine squadrons of six Rubis-class attack submarines at sea, with submarine crews divided into two groups and rotated every three months. 

The long-serving Rubis-class submarines are aging over time and have been replaced by Barracuda-class submarines in 2018, with all submarines due to be officially decommissioned by 2026