And they are VERY silent - precisely in order not to be detected by other submarines. In the long run, we're all dead. John Maynard Keynes
Maybe it was a joint exercise (presumably hide and seek games), or the submarines were in fact much closer to their home ports (where routes are presumably less varied), or it is sheer bad luck.
The fact is, these things are damn invisible to one another, if they are really inhiding mode, and they are also damn big. The probability of a collision is low but not toally absurd. In the long run, we're all dead. John Maynard Keynes
The Triomphant was only a couple of days from l'Ile Longue, so we know it was in the Gulf of Gascony. And it was a scheduled return apparently, this is near open-info from the french ministry. The Triomphant was coming back from the north atlantic (because the M45 missiles have a short range, we still need to be there to shoot moscow, old habits die hard).
The Vanguard has longer-range Tridents and should be patrolling a larger zone for better security, so I have no reason to question it's presence so far south of its base (the UK territorial waters in the atlantic are too small to be safe, in contrast to the US waters in the pacific, so UK boomers have to roam the open, whereas US subs keep hiding in their own waters around some archipelago of tiny desert atolls in the aleutians for instance, making collisions and stalking impossible for the russians) Pierre
But, yeah, there are attack submarines whose job is to try to hunt and kill boomers in event of war, so boomers aren't doing their job if they are relying on active sonar rather than passive sonar most of the time. And of course, each of them would be looking for ways to avoid being caught on passive sonar themselves. I've been accused of being a Marxist, yet while Harpo's my favourite, it's Groucho I'm always quoting. Odd, that.