HMS Defender was sailing from Odessa in southern Ukraine to Georgia. To get there, it passed south of the Crimea peninsula, which Russia annexed from Ukraine in 2014 in a move that has not been recognised internationally.
While Moscow claims the peninsula and its waters are Russian territory, the UK says HMS Defender was passing through Ukrainian waters in a commonly used and internationally recognised transit route.
BBC defence correspondent Jonathan Beale was on the deck of HMS Defender in the Black Sea as it was harassed by Russia's military.