A Royal Navy Type 23 frigate was involved in a collision at sea when a piece of the ship’s underwater tracking equipment came into contact with a Russian submarine, it has been revealed.
HMS Northumberland's sonar apparatus was struck while deployed underwater by a vessel it was tracking in the North Atlantic in late 2020.
The collision has been revealed by a Channel 5 documentary, the filming of which coincided with the incident, and which defence sources described as "extremely rare."
The television documentary series is called Warship: Life at Sea, and is currently airing on Monday evenings, with the episode featuring the incident due to be broadcast later this month.
A Royal Navy source has confirmed that the collision happened, saying: "It's unfortunate that the tracked item came into contact with the equipment tracking it, causing HMS Northumberland to return alongside."
In the episode, HMS Northumberland is filmed as she is forced to end her patrol early following the collision, returning to Scotland for essential repairs.
One former navy commander with considerable knowledge of the sonar equipment and type of patrol HMS Northumberland was undertaking at the time questioned whether the incident was an accident.
"Maybe it wasn't an accident."
Speaking to Forces News, Former Royal Navy Commander Tom Sharpe said the collision could have been a deliberate act by the Russian sub.
He said: "That class of frigate, well operated and well run, is very, very stealthy. It's possible the submarine was closer than it thought it was.
"Otherwise, you start tending to think that maybe it wasn't an accident. Maybe it was deliberate. I don't want to cause mischief, but that has happened before so that's an option in this case."
The equipment in question is called a Towed Array. Type 23s like Northumberland use them to detect underwater threats while on patrol.
It works by being tethered to the ship's stern and extended out at distances of up to two miles. Fitted to the array is sophisticated sonar equipment, which, in this incident, was in a collision with the Russian submarine.
HMS Northumberland was tracking the underwater vessel at the time of the incident. Yet, it is unclear whether the submarine was damaged in the contact or remained in the area following the frigate's departure.
Nevertheless, Mr Sharpe said towed arrays are not insignificant bits of kit and more likely than not, the Russian crew would have felt the impact.
He said: "These are huge bits of kit. The towed array on its wheel is vast and weighs tonnes, and it's very complex. Within it is a great array of equipment and wires."
A Ministry of Defence Spokesperson said: "In late 2020 a Russian submarine being tracked by HMS Northumberland came into contact with her towed array sonar."
"The Royal Navy regularly tracks foreign ships and submarines in order to ensure the defence of the United Kingdom."
Warship: Life at Sea is currently airing on Channel 5 on Mondays at 9 pm. The episode featuring the collision will be broadcast on January 17. Cover image: MOD.