France was the fourth country to join the so-called “Nuclear Club,” and at the height of the Cold War maintained its own nuclear triad of land-based missiles, nuclear-armed bombers and ballistic missile submarines. Today, France’s sea-based nuclear deterrent is the home of most of its nuclear arsenal, with four nuclear-powered ballistic missile submarines, of French design and construction, providing constant assurance against surprise nuclear attack.

France’s nuclear weapons arsenal began in earnest on February 13th, 1960, with the country’s first nuclear weapons test. The test, code-named “Gerboise Bleue” (Blue Desert Rat) confirmed that France had the know-how to build its own weapons. It also confirmed that France had the nuclear know-how to part ways with the United States and NATO and chart its own course versus the Soviet Union.

France began working on its own naval nuclear propulsion program in 1955, under what was known as Project Coelacanth. The first effort to build a nuclear-powered submarine, Q.244, was to be the first of five nuclear ballistic missile submarines. The effort to develop Q.244 was a failure, due to the inability of nuclear engineers to sufficiently miniaturize the reactor, and the submarine was cancelled in 1959. A subsequent project to develop a land-based reactor, PAT 1, was a success and led to development of Q.252, which became the submarine Le Redoutable.

At the same time, France’s defense industry was working diligently to produce a submarine-launched ballistic missile. The result was the M1 MSBS, or Mer-Sol Balistique Stratégique (Sea-Ground Strategic Ballistic Missile). The M1 was a two stage rocket with a 500 kiloton warhead and a range of 1,553 miles. This was sufficient range for a French ballistic missile submarine in the Bay of Biscay to strike Moscow.

France’s first generation missile submarines, the five submarines of the Le Redoutable class and the single L'Inflexible submarine, were all built at the Cherbourg shipyards and completed between 1971 and 1980. The cancellation of Q.244 may have been fortuitous, as it allowed the United States to make pioneer engineering decision in nuclear ballistic submarine design, something also seen in the Soviet Union’s first generation Yankee-class ballistic missile submarine. The overall layout of the Redoutable class was very similar to the U.S. Navy’s second generation Lafayette-class ballistic missile submarines, with fin-mounted hydroplanes and sixteen missile silos in two rows of eight directly behind the fin.

The first two submarines, Le Redoutable and Le Terrible, carried the M-1 missile, while the third, Le Foudroyant, carried the improved M-2 missile with a longer 1,841 mile range. The next two submarines, L’Indomptable and Le Tonnant had a mix of M-2 missiles and the new M-20, which had the same range but a gigantic 1 megaton thermonuclear warhead. The last submarine, L’Inflexible, carried missiles of a completely new design. Designated M4, the missiles had a 2,474 mile range, allowing them to strike as far east as Kazan.

At the height of France’s nuclear weapons arsenal, 87 percent of France’s nuclear arsenal was in submarines. France’s nuclear submarine fleet, the Force Océanique Stratégique (FOST), was based at Ile Longue in Brest, and FOST submarines were sent on two month patrols off the coast of France and Portugal. Three submarines were to be at sea at any one time, with a fourth also ready to go to sea.

Starting in the mid 1980s, all submarines except for Le Terrible were outfitted with improved M-4A and then M-4B missiles with ranges of up to 3,720 miles and multiple independently targetable reentry vehicles, allowing each missile to carry six 150 kiloton warheads. The MIRVing of the M4 increased the firepower of each submarine sixfold.

In addition to their nuclear firepower, the Redoutable class submarines had four 533-millimeter torpedo tubes for self-defense, capable of launching the L5 Mod. 3 anti-submarine torpedo and the F 17 dual-purpose torpedo. They could also launch the SM 39 Exocet anti-ship cruise missile, but the primary mission of ballistic missile submarines is always to avoid detection until their nuclear missiles are needed.

France’s second generation missile submarines, the Triomphant class, were built between 1986 and 2010, a remarkably long timeline for just four submarines but par for the course for post–Cold War shipbuilding. The first in class, Triomphant, began construction in 1986 and was finally commissioned in 1997 while the second, Téméraire, entered the fleet in 1999. The third boat, Vigilant, was commissioned in 2004 while the fourth and final boat, Terrible, was commissioned in 2010.

The Triomphant class is larger than the earlier generation submarines, and indeed shares the same nuclear reactor, the K-15, with the nuclear aircraft carrier Charles de Gaulle. The first four ships in class were originally armed with the M45 intermediate-range missile, a solid-fuel design with a range of 3,728 miles. The M45 had an identical loadout to the M4B, carrying six 150-kiloton MIRV warheads, but included penetration aids to overcome ballistic missile defenses.

The last submarine, Terrible, was the first equipped with the current missile, M51. M51 has the same number of six 150 kiloton warheads but goes a step further in defeating ballistic missile defenses as each warhead is capable of independent maneuvers during the terminal descent phase. M51 has a range of nearly 5,000 miles. The new missile is being gradually retrofitted to the entire French ballistic missile submarine fleet.

The resurgence of Russian military power—and the will to use it—will likely keep Paris a nuclear power for the foreseeable future. As small as it is, France’s nuclear arsenal is not designed to win a nuclear war, just not lose one. France’s four nuclear missile submarines will ensure that.

Kyle Mizokami is a defense and national-security writer based in San Francisco who has appeared in the Diplomat, Foreign Policy, War is Boring and the Daily Beast. In 2009 he cofounded the defense and security blog Japan Security Watch. You can follow him on Twitter: @KyleMizokami.

Image: A view shows the submarine "Le Terrible" whilst at sea during a visit by French President Emmanuel Macron to the vessel, July 4, 2017. Picture taken July 4, 2017. REUTERS/Fred Tanneau/Pool