LONDON – A towed array sonar deployed by a Royal Navy frigate hit a Russian submarine during operations in the North Atlantic in 2020, the British Ministry of Defence has confirmed.

The Type 23 anti-submarine frigate HMS Northumberland was tracking the submarine in late 2020 when the collision occurred.

The incident was recorded by a film crew for the British TV station Channel 5 for a documentary series called “Warship: Life at Sea” that is now showing in the U.K.

The TV crew record the moment the ship’s crew spot what they believe is a submarine periscope and communication mast breaking the surface.

The warship’s commander can be heard at one point saying the submarine is very close to HMS Northumberland.

“We are probably parallel. If they were on the surface, we would definitely see faces,” he is recorded as saying.

Following the incident the British launched a Merlin anti-submarine helicopter to try and locate the Russian boat.

Sources say there was no suggestion the collision was deliberate as there was no way the Russians would have known the array was there.

The incident was confirmed by the MoD. “In late 2020 a Russian submarine being tracked by HMS Northumberland came into contact with her towed array sonar,” said a spokesman.

“The Royal Navy regularly tracks foreign ships and submarines in order to ensure the defense of the United Kingdom,” he said.

The British warship was forced to return to base to replace its Thales UK-built Sonar 2087. It is not known if the Russian submarine was damaged.

A towed array consist of a cable with a long cluster of sophisticated sensors at its end. In layman’s terms, it is a plastic tube the diameter of a person’s fist filled with super sensitive microphones (transducers) pulled through the water by the warship.

The sonar has passive and active modes of operation and it was the former array that was damaged.

Nick Childs, a senior fellow for naval forces at the International Institute for Strategic Studies think tank in London, said the incident was highly unusual but not unique, with advances in uninhabited technology potentially leading to similar incidents.

“The likelihood is that it was an accident, since towed arrays are not easy for a submarine to detect precisely, and there would have been some risk to the submarine from a deliberate collision,” he said.

“However, there is a report of at least one incident from the Cold War of a British nuclear submarine, HMS Conqueror, cutting and capturing a towed array from a Soviet ship, but the submarine was reportedly specially modified and equipped for the job,” said Childs.

The incident is reminiscent of the era’s secretive submarine operations between the West and the Soviets, he added.

“During such missions, these U.K. and U.S. submarines, and presumably Soviet ones as well, often got extremely close to their prey, with one reported example of a U.K. submarine getting right up under the keel of a Soviet aircraft carrier in order to photograph its underwater hull.

“This latest incident could be seen as an indicator that such operations are now very much back on, so potentially the chances of one happening again is increased,” Childs said.

Andrew Chuter is the United Kingdom correspondent for Defense News.

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