Ironically, the British and French nuclear submarines—the last line of defense in their respective arsenals—were so undetectable that they failed to spot each other until they collided.

On the night of February 3–4, 2009, the United Kingdom’s HMS Vanguard and France’s Le Triomphant, two nuclear-powered ballistic missile submarines, collided while submerged in the Atlantic Ocean. 

It was an almost impossible accident. Mathematically, the laws of probability dictated that in a body of water as enormous as the Atlantic, a collision between two small vessels would be extremely unlikely to occur. Yet it did happen: the two British and French nuclear-powered ballistic missile submarines (SSBNs), both equipped with nuclear weapons and tasked as the ultimate guarantor of a second-strike capability in their respective nations’ arsenals, were designed to be as stealthy as possible, and as a result did not see each other in time to avoid a collision.

Fortunately, both vessels were moving at an extremely slow speed, and there were no reported injuries, nuclear leaks, or compromises of the safety of the nuclear weapons aboard. Both vessels returned to their respective nations safely and were able to undergo repairs, and both remain in service; there is no word if procedures were changed following the incident.

The Submarine Collision Was a Freakishly Low-Probability Accident

HMS Vanguard (S28) is the lead boat of the UK’s four-ship Vanguard class of nuclear-powered ballistic missile submarines. Designed to serve as London’s sea-based nuclear deterrent leg, the Vanguard class can carry up to 16 Trident II D5 submarine-launched ballistic missiles (SLBMs). At the time of the accident, the submarine was carrying a crew of approximately 135.

The French submarine involved in the accident, Le Triomphant (S616), was the lead boat of France’s four-vessel Triomphant class, and at the time of the accident, was carrying approximately 111 sailors. Like the Vanguard, Le Triomphant was also capable of carrying up to 16 M45 SLBMs. Between the two boats, that’s two nuclear reactors and scores of nuclear warheads, all in close proximity during the collision. 

So what exactly happened? The details remain unclear, as SSBN patrol locations and operations are closely guarded military secrets. (For obvious reasons, the United Kingdom and France do not coordinate nuclear submarine activity, helping to enable the crash.) However, it is known that the Vanguard was conducting a routine patrol, while Le Triomphant was returning from one, when the two collided.

France initially announced on February 6 that Le Triomphant had struck an unidentified submerged object, thought perhaps to have been a shipping container. The full story only emerged later, with British First Sea Lord Admiral Sir Jonathon Band confirming the submarine collision on February 16.

How Much Damage Did the Collision Cause?

Vanguard suffered damage to its starboard outer casing around the missile compartment, while Le Triomphant suffered damage around its bow and active-sonar dome—suggesting that the French vessel accidentally rammed into the British one. Both remained seaworthy, however, and returned to their respective bases under their own power. Reporting suggested the repairs could have cost as much as £50 million, or roughly $73 million in 2009 (about $106 million today).

It is clear, however, that the accident could have been far more consequential, both in terms of loss of life and nuclear leakage. Both submarines weigh in excess of 14,000 tonnes; at a higher speed, the amount of kinetic energy transferred between them by a sudden impact could have destroyed both.

The presence of nuclear reactors and ballistic missiles remains one of the most alarming aspects of the collision. Anti-nuclear campaigners seized the opportunity to warn that the collision could have produced radioactive contamination or problems involving the weapons aboard. British authorities claimed that nuclear safety was never compromised. But who knows?

Ultimately, the 2009 collision is one of the stranger stories in submarine warfare. The United Kingdom and France both spent enormous sums engineering submarines capable of disappearing into the Atlantic. The irony is that both nations accomplished the feat so well that the two submarines couldn’t even detect one another at close range. While the collision didn’t cause casualties or nuclear release, it exposed the problems inherent to loading up a secretive and stealthy platform with nuclear material. That nothing catastrophic happened is a small saving grace. And the likelihood of such a collision happening again is statistically low—but, as the original accident demonstrates, not zero. 

About the Author: Harrison Kass

Harrison Kass is a writer and attorney focused on national security, technology, and political culture. His work has appeared in Tablet, City Journal, The Hill, The Spectator, and The Cipher Brief. He holds a JD from the University of Oregon and a master’s in Global & Joint Program Studies from NYU. More at harrisonkass.com.

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