First Sea Lord Admiral Sir Ben Key said the hunter-killer submarines – called SSNs – were confined to port on the same day in September.
MPs branded the situation “embarrassing” as it meant British waters and shipping would not have been protected from Moscow’s vessels if they were in the North Atlantic.
At the Commons Defence Select Committee, former defence minister Mark Francois blasted: “We didn’t have a single one at sea, I think, for the first time in living memory. That is operational failure, isn’t it?”
But Adm Sir Ben replied: “I refute that. There was no need for any of those submarines to be at sea.”
The subs docked in Plymouth, were HMS Astute, Ambush, Artful, Audacious, Anson and Triumph.