A Russian submarine collided with a Royal Navy warship on patrol in the North Atlantic, the Ministry of Defence (MOD) has confirmed.
HMS Northumberland had been tracking the submarine when it hit the ship's sonar - a piece of equipment being trailed hundreds of metres behind it.
The incident, in late 2020, was captured by a television crew filming a documentary.
A UK defence source said it was unlikely the collision was deliberate.
The MOD said the frigate had located the submarine using the towed array sonar - a long tube fitted with sensitive hydrophones to listen under the water.
A periscope was spotted before the Russian submarine dived again, hitting HMS Northumberland's sonar.
The cameras for Channel 5's Warship: Life at Sea captured the crew shouting: "What the hell was that?".
It is not clear what, if any, damage was suffered by the Russian vessel but the warship had to return to port to replace the damaged sonar.
There has been an increase in Russian submarine activity in recent years, and Royal Navy frigates regularly patrol the North Atlantic.
The MoD would not usually comment on operations but it has been made public this time because the incident was caught on camera.
A spokesman 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."