A British naval supply ship with an on-board helicopter was deployed to track the stealthy Kilo-class submarine Krasnodar, the Royal Navy said.

The Russian submarine was allegedly carrying Kalibr cruise missiles, which Russia has used in devastating strikes on critical infrastructure and military targets across Ukraine. The SBU said the submarine was “put out of action” as a result of the blast. The FT could not independently verify the claim.

Russia’s Kilo-class submarines may be Cold War designs, but they remain at the core of Moscow’s conventional undersea fleet. -Nicknamed “Black Holes” for their extreme quietness, modern Project 636.6 Improved Kilos combine diesel-electric stealth with long-range Kalibr cruise missiles,