A warship of the British Royal Navy had a collision with a Russian submarine it was tracking that had unexpectedly disappeared from the ship's radar. The run-in shocked the sailors onboard and their reactions happened to be captured by a documentary crew with Britain's Channel Five news network.

The incident took place towards the end of 2020 when the HMS Northumberland was on patrol in the North Atlantic, tracking a Russian hunter-killer submarine that had appeared inside the Arctic Circle.

The Northumberland's captain ordered the crew to close in on the Russian submarine, stopping just about parallel to it where the Russians would be able to detect it and know that they were discovered. However, the frigate stopped at a safe distance to avoid alarming the Russians into taking any sudden actions.

It is a routine task for the Royal Navy to shadow and monitor Russian vessels that stray beyond their Arctic naval bases, but the Northumberland’s mission got complicated when the submarine disappeared from its radar. But then, it reappeared with a thud.

“What the hell was that?” British sailors can be heard asking at the 1:42 mark in a clip of the documentary, shared by the London Evening Standard.

One of Northumberland's towed array sonars, a tube-like device fitted with microphones that listen underwater, had bumped into the Russian submarine a few hundred meters behind it. Just before, the frigate's helicopter reported spotting a periscope before the sub plunged underwater to avoid detection.

After the encounter, the Northumberland made its way back to its base in Scotland to replace the damaged sonar. The frigate itself was not damaged and it is unknown if the Russians sustained any damage.

Encounters at sea between the Royal Navy and their Russian counterparts can be testier than the one endured by the Northumberland and its crew. Last June, the HMS Defender was shadowed by Russian vessels in the Black Sea and fighter jets were scrambled as the Defender passed the coast of the Russian-occupied Crimean Peninsula. Russian defense officials said that they fired warning shots at the Defender and President Vladimir Putin accused the U.K of being deliberately provocative.