There’s an old Navy saying …

A collision at sea can ruin your day.”

It can also ruin several careers. One of the “related content” articles says:

    One theory being considered was that their respective anti-sonar devices – which hide submarines – were just too effective in concealing one from the other.

Possible. Not necessarily likely. Both submarines are identified as SSBNs – ballistic missile launch platforms, rather than attack submarines. This means that, rather than actively “pinging” with their sonars and listening for echos, they were listening passively to what their sonar arrays were picking up.

Sound travels long distances and in funny ways in the ocean, and it’s not necessarily a very quiet environment. The article mentions rough seas – there was probably a lot of wave noise as background. Living things make a wide variety of sounds – for years, there was an unidentified noise that sonarmen referred to as “the A-train.” I believe it was eventually attributed to Minke whales, but I could be misremembering. The path sound takes in the ocean is dependent on water temperature, salinity, and pressure, and can curve in such a way that you could be travelling parallel to another vessel that is relatively close and never hear it. You could also hear it and think it’s in a different direction compared to where it really is.

There are also blind spots in a submarine’s sonar array. For one thing, you can’t hear behind you, both because the sonar array doesn’t usually have any elements pointing directly aft, and because any that point aft would mostly pick up your own propulsion sounds. Periodically, a submarine will “clear baffles” by putting a wiggle into its track, changing course for a minute or two so that the sonar will be able to “see” behind it, then coming back to its original course.

The description of the results of the collision leads me to believe that the French sub ran into the side of the British sub. I saw nothing to indicate what angle the collision occurred at. First Sea Lord Admiral Sir Jonathan Band said that it was a low-speed collision, so it was probably just bad luck. It could have been worse – much worse.

Returning from patrol, there comes a point when you no longer have to hide your presence, and are allowed to make more speed. There is a tendency to request “going-home turns” from the engine room. Had that been the case, with the French submarine coming up in the other sub’s baffles, the collision could have been much worse. I’m glad it wasn’t.

    Eternal Father, strong to save,
    Whose arm hath bound the restless wave,
    Who biddest the mighty ocean deep
    Its own appointed limits keep;
    Oh, hear us when we cry to Thee,
    For those in peril on the sea!

UPDATE: Blackfive and Neptunus Lex have also reported on this story. The comments at Blackfive are more amusing, but the ones at Neptunus Lex are more informative.

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