How Ukraine's stealthy sea drones strike Russian targets

President Zelensky has described seaborne drones as Ukraine's "eyes and protection on the frontline", with claims of a series of successful strikes against Russian ships in the Black Sea and on a key bridge to Crimea. These remote-controlled devices are playing an increasingly prominent role, with both sides ramping up their use for attacks and reconnaissance. The BBC's Security Correspondent Frank Gardner and BBC Verify examine their influence on the conflict.