Jeffrey LewisWhen SSBNs Collide

Greetings from Chicago, where I am about to give a talk at the AAAS Annual Meeting on open source intelligence and blogging.

This is embarrassing for the Royal and French Navies:

Royal Navy nuclear submarine was involved in a collision with a French nuclear sub in the middle of the Atlantic, the MoD has confirmed.

HMS Vanguard and Le Triomphant were badly damaged in the crash in heavy seas earlier this month.

First Sea Lord Admiral Sir Jonathon Band said the submarines came into contact at low speed and no injuries were reported.

Both the UK and France insisted nuclear security had not been breached.

Despite being equipped with sonar, it seems neither vessel spotted the other, the BBC’s Caroline Wyatt said.

The Daily Mail claims
that the seas were very rough and Le Triomphant was returning from patrol. Le Triomphant was amble to limp home. HMS Vanguard had to be towed.

I find this statement, that the SSBNs just happened to randomly bump into one another, interesting:

“This is clearly a one-in-a-million chance when you think about how big the Atlantic is,” [Wyatt] said. “It is actually unbelievable that something happened.”

I wonder about that. When something is, statistically speaking, unbelievable, I usually don’t believe it. But I don’t have a better hypothesis right now.


  1. Rwendland (History)

    CNN seem to have a fuller statement by the French:

    “Two “SNLE” (nuclear submarines), one French and the other British, were, a few days ago, on standard patrols in the Atlantic. They briefly came in contact in a very slow speed while they were immersed. There is no casualty or injury among the crew. Neither the nuclear deterrent mission nor the nuclear security have been compromised,”

    So the French claim they wer on standard patrol, and the UK MOD claim UK’s deterrent capability had “remained unaffected at all times.”

    Wonder if we will ever get to know more.

  2. Andreas Persbo

    It’s the French getting even for Trafalgar.

  3. Gridlock (History)

    It’s fairly easy to explain when you remember that the Senior Service and Le Navy are on.. less than friendly terms*. My guess would be that one or the other picked up the fellow boomer and decided to try for a little sneaky shadowing, just to prove the other side wanting.

    * The French don’t like to discuss their history with the RN..

  4. blowback (History)

    No doubt the French and British have done extensive hydrographic surveys of the Atlantic sea floor and have identified the best routes for their submarines to transit to and from their patrol areas. Given both navies need to keep their subs hidden it is highly likely that they use similar routes, so the chances of them hitting each other are probably not that remote.

  5. scud

    S***t happens. Factor in the number of French and British patrols in the past 40 years, the fact that they have to “share” the waters before actually reaching their patrol areas, and you get a non-negligible (though very small) risk of incident, it seems. I cannot see any reason why they would be deliberately next to each other. At least this should put an end to the tiresome rumours which have been going on for decades, according to which the two countries coordinate their patrols.

    It would be interesting for wonks to compare the probability of two SSBNs to collide with that of, uh, satellites.

    In any case, reliable French sources say that it was only a fender-bender.

  6. Omid (History)

    It seems that we’re in the collision month!

  7. anonymous

    My guess is that they were conducting a joint tracking exercise of some kind.

  8. Lucas Fischer (History)

    It may be that UK and Fr SSBN patrol areas are close to each other, or that their transit routes from those areas are similarly close (e.g., if they patrol around the North Cape, each would have to transit back around the north end of Scotland .)

  9. Nick Nolan (History)

    It’s not like this has not happened before

    My hypothesis is that other was stalking the other. Of two ships that pass in the night, other (Le Triomphant) gets sonar reading and starts to investigate. They get closer and closer (from behind), until something happens (they get too close, then lose the stalked ship momentarily behind inversion layer before collision, etc.)

    I can also imagine that great intelligence gathering idea like “Hey let’s see how close can we get” before we are noticed” might have contributed to the crash.

    ps. I assume that Le Triomphant was coming from behind because it was not the one who needed towing.

  10. pkr (History)

    The Royal Navy has issued the following statement: “Two submerged SSBN, one French and the other UK, were conducting routine national patrols in the Atlantic Ocean. Recently, the two submarines came into contact at very low speed. Both submarines remained safe and no injuries occurred. We can confirm that the capability remained unaffected and there has been no compromise to nuclear safety. HMS Vanguard returned safely to Faslane under her own power on 14 February.”
    The BBC simply echoes the initial report by the Sun that appeared on Monday stating that the Vanguard “was last night towed into Faslane in Scotland, with dents and scrapes visible on her hull.” Accurate information is obviously limited to the official announcements of both sides…

  11. Tim (History)

    This event makes it clear that either French or Brittish submarines are equipped with improbability drives. We must act quickly to close the improbability gap!

  12. F.

    “This is clearly a one-in-a-million chance when you think about how big the Atlantic is,” [Wyatt] said. “It is actually unbelievable that something happened.”

    I doubt that, too. The one-in-a-million-chance is probably only right if you consider every possible route in the Atlantic as equally likely to be taken, i.e. random SSBN cruising in the ocean… But aren’t there some routes that are more frequented than others, for example the shortest way from A to B?

    Sure, even if that would raise the likelihood of such a thing to happen, it would still be very unlikely. In the end, the ocean is still quite big…

    But as another ship commander wisely observed a long time ago:
    “Never tell me the odds.”

  13. Lucas Fischer (History)

    Second comment: re the sonar, this is not surprising to me; I would not expect SSBNs on an operational patrol, even in transit, to be pinging with active sonar. They’d presumably be listening with passive sonar, but other SSBN’s would be pretty quiet even at transit speeds; and if they were not running very deep, wave noise would be a problem.

  14. Derek (History)

    According to a BBC article on the incident:

    “Both navies want quiet areas, deep areas, roughly the same distance from their home ports. So you find these station grounds have got quite a few submarines, not only French and Royal Navy but also from Russia and the United States.”

    Evidently there are preferable areas in which to deploy and stage SSBNs near Europe. The French and British finally found something on which they both (inadvertently) agreed.

  15. Allen Thomson (History)

    Several times during the Cold War there were submarine-submarine interactions, but they were generally caused by an SSN trying to sneak up on another sub for purposes of intelligence gathering.

    Probably not a good idea in any case, but certainly not a good idea to use an SSBN for such purposes, if that’s what happened.

  16. Major Lemon (History)

    Rubber(anechoic)sonar absorbing tiles are supposed to have caused this. Actually it’s not such a ‘coincidence’ despite the vastness of the Atlantic. There are tight patrol routes that the various navies like to cover. Funny, just the other day when we were talking about colliding satellites, someone rather flippantly made the comment ‘worse things happen at sea’. Thankfully with this latest incident, the cost wasn’t anyone’s life.

  17. Yale Simkin (History)

    If one of the boats was an attack boat and the other a boomer, then I could see this as an error during a cat and mouse game (with the mouse unaware of the game).

    Both being missile boats is more mysterious.

  18. FSB

    So it would appear that the reliability of the nuclear warheads may not be the weakest link in the reliability of these weapons systems. Seems like other more mundane modernizations are more important than making unnecessary RRWs.

  19. John Bragg (History)

    “This is clearly a one-in-a-million chance when you think about how big the Atlantic is”

    Deceptive, since the issue is how big the Bay of Biscay is. Or really, how big the number of good SSBN areas there is. More like 1 in 1000, or even 1 in 100.

    Which is to say, inevitable given time and no Anglo-French coordination.

  20. Tim Kelly (History)

    “Saunders said submarines don’t always turn on their radar systems or make their presence obvious to other shipping.”

  21. Purple Clarinet

    Basically two scenarios appear to look plausible based on the limited information currently available in the public realm (…apart from our ´official´ explanation of the one in a million chance mishap. LOL):

    1. Vanguard and Le Triomphant were engaged in a highly classified military exercise probably aimed at creating a certain capability of being able to conduct joint patrols/maneuvers of RN SSBN’s and MN SNLE’s. Obviously both crews had not the necessary experience (and precise information?) about each others tactical/technical ´modus operandi´ and consequentially the entire operation went badly wrong. Of course a substantial cooperation between France and the UK in the strategic field would be a highly sensitive subject for Paris as well as for London and especially Sarkozy would have probably pressed for strictest secrecy of the whole affair. So both governments are simply dishing up just the usual disinformation tales…

    2. Le Triomphant was able to limp home on her own power but sustained heavy damage in her sonar bow whereas Vanguard was apparently extensively damaged at the side of her hull and had to be towed into base.

    Naturally this is speculation but perhaps Vanguard was ´shadowing´ the homebound Le Triomphant thereby testing her newest sonar equipment. Vanguard got a new side sonar during her latest dockyard period and accordingly her sonar capabilities should have been superior to Le Triomphant’s (Though this would be an interesting point of debate! Any experts on British or French sonar systems?)

    Furthermore such a little ´cat and mouse´ game would also prove satisfactorily that the venerable RN is still in the lead in comparison to the (in usual RN perception!) ´mediocre´ Marine Nationale. Unfortunately the French commander took a surprising turn and probably Le Triomphant was somewhat more agile and quiet than anticipated by the British crew and the crash was suddenly unavoidable. This scenario would imply that only the RN SSBN was actually aware of the situation and would put responsibility for the accident fully on the RN. At least the public performances of several obviously highly embarrassed RN admirals and the conspicuous two week kong silence by the MoD should be enough reason for getting justifiably suspicious.

    Sarkozy will be certainly not amused…

  22. Maggie Leber (History)

    The “random bump” theory seems more plausible than “a boomer decided to play attack sub”.

    Been a big month for random collisions.

  23. Alex (History)

    SSBNs use certain routes for their patrol cruises. Apparently both vessels chose the same safe route because of certain weather conditions, which contributed to the incident. Considering that we are speaking of military allies here, who share strategic information like nautical data, the whole incident does not seem to be so absurd anymore.

    Its still remarkable, since UK and F both only have got one active SSBN on patrol at a given time. But unbelievable…I dont think so.

    The mass media is having a field day though…

  24. John F. Opie (History)

    Hi –

    Part of the problem, of course, is that both subs are extremely quiet: normal sub operations use passive sonar to listen to what is coming their way. Neither the British sub nor the French sub could be picked up on the others’ passive sonar system (otherwise they’d have heard the other sub!).

    It’s worse than driving at night with your lights turned off. It’s more like driving at night with the lights turned out and the windshield painted black, listening to the road noise.

    So yes, I fear that it is simply an accident, a random encounter on travel routes commonly used by such subs. I can well imagine that these routes will now be under review to avoid even the remote possibility of this happening again…

  25. thermopile

    A few distantly connected points:

    1. With ever-tightening budgets, it wouldn’t surprise me at all if SSBN’s were occasionally being used for more traditional SSN roles. Like sub tracking, for instance. I don’t believe the French Defence Minister, Herve Morin, when he denies to Reuters that either country engages in sub tracking.

    2. Can anyone confirm if this was a head-on collision? I can’t find any published reports of where the damage is. If it was head-on, that makes sub tracking a little less plausible, and my third point slightly more plausible…

    3. Another theory is that the two subs were both scared to a known “safe place” by a common, third enemy. Hypothetically, a Russian surface ship went active, and both subs dove for a thermocline near an undersea mountain range. I have no evidence to support this, but it is interesting.

  26. Jeffrey Lewis (History)

    I’ve seen reports that weather was rough and that the French submarine was diving.

    Le Monde had a statement that this is the first time this has happened in approximately 400 patrols — a nice piece of data.

  27. scud

    Just a quick second comment for those who mention the hypothesis that the two countries were doing some kind of joint exercise, or that one of them was playing a “cat and mouse” game. This is nonsense. In normal times, France and the UK have only one SSBN at sea. The number one priority (and the only one in fact) for the SSBN commander is to go deep, go silent, and ensure his deterrent patrol in good conditions. SSBNs do NOT play cat-and-mouse games on each other. SSNs vs. SSBNs do. Period. And that’s the case for all countries which have SSBNs.

  28. Stephen Young (History)

    Re: 400 patrols, just learned from a reliable source that the U.S. Navy will be celebrating the 1,000th Trident patrol later this week.

  29. Alex (History)

    The subtracking theory has been raised elsewhere on the net. On this issue I completely agree with scud. As was pointed out before, UK and F both have only one SSBN available for deterrence missions. Risking the only active boomer like this just for tracking an allied boat seems more than a bit absurd to me.

    As for the type of collision…it seemed to me that the french boat ran behind and into the UK boat. Thats why Le Triomphant had a dented sonar dome but could make it back to port under her own power, while the british boat had to be towed back home (rudder and/or propulsion damage).

  30. Purple Clarinet

    Of course bumping into each other at patrol depth on ´silent run´ mode in the middle of the vast North Atlantic is obviously the most self evident explanation for this kind of ´peculiar´ incident. Please forgive me of not being equally gullible…

    Some bits in the French media appear to indicate that indeed a highly classified joint RN/MN maneuver including also several SSN’s was going on in the area (…at least the MN was prepared to keep the entire incident completely under wraps until the British press got wind of it).
    For reasons we can only speculate about (e.g. lack of experience in joint sub operations, insufficient technical information etc.) things (exactly abiding ´Murphy’s law´!) got badly awry. After all this would be at least an explanation of the affair not prone to stretching the limits of probablility…

    Possibly the upcoming inquiry report will provide the public with some verifiable facts but I would not bet on this.

  31. WillieNillie

    The French have 4 Triomphant-class SSBNs. It was said in the French media that another one was already on patrol at the time of the incident, so nuclear deterrence was not discontinued.

    That would also indicate a joint exercise.

    Maybe were the RN was helping the MN testing the new Le Terrible SSBN that just came out this year??

  32. scud

    @Purple Clarinet:

    – I have not seen any report in the French press about “joint sub operations” (even though I monitor French press closely), but what one can say is that the whole idea of a “joint patrol” or of an “exercise” makes absolutely no sense. Again, when they have only one SSBN on patrol on a permanent basis, both countries want their SSBN to do one thing, and only one: to be on patrol. Period. And to the best of my knowledge, no country has ever “joint SSBN operations”. The very concept does not even begin to make sense. SSBNs do not want to be next to each other. They do not do “exercises” with other ships, except during trials when they are not yet operational. Which was not the case for Le Triomphant.

    – You underestimate the probability of a FR and UK SSBNs to be in the “same waters”. SSBN commanders look for the same kind of waters, those where the accoustic characteristics minimize the chances of detection.

    Please do not fall for conspiracy theories. The probability was very, very low, but not lower than winning the grand prize at the lottery.


    – You mention Le Terrible, but assuming it was at sea it had nothing to do with the incident. By definition it would have been far away from Le Triomphant.

    – Assuming that there was a second French SSBN at sea – your conclusions are wrong. The way the French and the Brits do it is that in order to ensure continuous at sea deterrence, one sub leaves port before the other one returns to port. (They sometimes actually put out two SSBNs on patrol, but I see no reason why this was would have been the case at that time.)


    Once SSBNs have reached their patrol area, only the crew knows where it is and where it goes (unless there is… an accident). It’s the whole point.

  33. spaceman africa

    I have gotten second hand info from an Englishman that indicates both subs were diving due to inclement weather. It has also been confirmed that the French sub hit the Brit sub. Vigilant has been scrambled to take Vanguards station and Vanguard was “not damaged significantly.”

    My source also hedged their info in such a way as to make thermopiles third scenario equally likely.

    Thanks to scud for keeping things in perspective. I do like a good, somewhat outlandish, hypothesis as much as the next guy but like with all things there is a breaking point.

  34. Gridlock (History)

    FYI Vanguard didn’t need to be towed home, it was simply (as is standard) towed into port by tugs.

    [Thanks, I see the BBC story has been updated to reflect that. — Jeffrey]

  35. John Ainslie (History)

    I filmed HMS Vanguard as it was towed, between midnight and 3 am, from the covered jetty at Coulport to the shiplift at Faslane, where it is again concealed. Here it will be lifted out of the water so they can look at the damage underneath.

    The MoD are desparate that no-one should see it – but there was no visible damage on the top part of the submarine.

    Footage is on

  36. Hairs (History)

    “This is clearly a one-in-a-million chance when you think about how big the Atlantic is,” [Wyatt] said. “It is actually unbelievable that something happened.”

    Rubbish – it is highly believable that such an incident could indeed have occurred. As other ACW readers have pointed out, the topography and conditions of the ocean (e.g. depth of the thermocline) and, not least, the maximum operating depth of the submarines, significantly constrains the volume in which the subs could have been (or would have wanted to be) present.

    If you still think the remaining volume is too large then may I suggest you read Buchheim’s excellent “Das Boot”. Buchheim was posted on U-boats during WW2, and after the war wrote of his experiences, including how his boat and that of Thomsen very nearly collided in mid-Atlantic. In his introduction to the book he wrote, “This book is a work of fiction, but every word is true”, and many years ago I heard him confirm the truth of the near collision in an interview on German radio.

    In a similar vein, there is no shortage of ship collisions on the high seas every year even where each ship has been making all the usual efforts to see and be seen.

    It may eventually turn out that there were some games going on, but it is far from “unbelievable” that this incident was simply a chance event.

  37. Aaron Tovish (History)

    (1) Those who try to explain this in terms of limited patrol areas based on mutually preferred seafloor areas with suitable topography need to explain the reference to surface storm conditions. If Triomphe was returning to port (as some reports suggest), but Vanguard was still on patrol (as no report contests). Why were they at the same depth at all?
    (2) Those who say the practice is running silent and that very limited patrol areas overlap should explain why level-headed people didn’t realize that an accident was inevitable.
    (3) Those who think Triomphe was tailing Vanguard (despite all the logic and rules against it) — perhaps to test the Vanguard’s new radar — need to explain how the Triomphe found the Vanguard in the first place.
    These considerations lead to me to believe that there was a joint exercise that ran afoul. This would also imply that there will be no public explanation of the incident.

  38. kerbihan

    1) It is not a question of seafloor topography. It is a question of the waters’ characteristics (depth, salinity, etc.). Some places are more attractive than others when you want to be silent, especially when you’re on your way to (or returning from) your patrol area.
    2) An accident was surely not inevitable. The ocean is a very big place, and patrols areas are not that “limited”.
    3) Agree.
    …But those who believe that “there was a joint exercise” need to explain why on earth would it make sense for two SSBNs to do a joint exercise – in especially unaccompanied by SSNs, and – most importantly – when the two countries have only one SSBN at sea.

  39. Aaron Tovish (History)

    Let’s get a handle on the probability:
    Earth’s surface area: 40,000kmX40,000km/π
    2/3rd covered by water
    Percent of total sea area frequented by nuclear-armed submarines: (more or less??) 1%
    Operating depth range of subs: zero to 1000m?
    Percent of range frequented by subs: (more or less??) 10%
    Multiplying the above will give you the volume of ocean in which there are at any time (more or less??) 20 subs

    Cross section of sub: 100sqms
    Total number of patrols since beginning: (more or less??) 2000
    Average distance covered by patrols: (more or less??) 5000km
    Multiply these to get the volume of ocean traversed by subs thus far.

    If these volumes are comparable then a collision is not unlikely.

    Very roughly I get 10 to the 14 cubic meters of ocean containing 20 subs

    Very roughly I get 10 to the 9 cubic meters of ocean traversed by subs.

    That leaves a gap of about 10 to the 4, i.e. 10,000:1 odds of NOT hitting one of the 20.
    Use lower estimates to calculate the first volume and higher ones for the second and you can improve the odds. But there is still a long way to go to make it likely. And remember this is the likelihood during the entire span of the nuclear-armed submarine age.
    Use higher estimates for the former and lower for the latter and the odds go through the roof.

    If you compare this to satellite collisions:

    Earth’s surface area, altitude in 100 kilometers (not meters). Volume: 10 to the 19 cubic meters
    Cross section of satellites: 1-10 sqm
    Number of satellites: 1000?
    Numbers of orbits per year: 5000?
    Number of years: 50
    Length of orbit: more than 40,000km
    Volume: 10 to the 16
    Since there are 1000 targets, the odds are (very) roughly 1:1 over 50 years.

  40. Aaron Tovish (History)

    It would not surprise me at all if the nuclear-armed subs were doing something other than ‘deterring.’ This notion of being constantly vigilant was exaggerated even during the Cold War. Now it is downright is downright silly. Even if I allow that having one sub out of port at all times might make sense (not!), having it preoccupied 24/7 with readiness to launch a counterattack is a total waste of time and money. The ‘bolt-form-the-blue” scenario is a dead horse, why would one still be beating it?