Between March 2000 to July 2005 Kasatonov was captain of the battlecruiser "Pyotr Velikiy". It was during the Northern Fleet's annual exercises in the Barents Sea in August 2000 that the Oscar II-class submarine K-141 "Kursk" suffered a fatal accident and sank. The exercises, which began on 11 August, were the largest Russian naval exercises since the dissolution of the Soviet Union in 1991. More than thirty warships took part, overseen by the commander of the Northern Fleet, Admiral Vyacheslav Popov, with the "Pyotr Velikiy" as his flagship. On the morning of 12 August, the "Kursk" was scheduled to make a dummy torpedo attack on the "Pyotr Velikiy". During preparations for the attack, the "Kursk" suffered an explosion and fire in her torpedo room, followed by a second larger explosion that sank her. Kasatonov's sonar operators aboard the "Pyotr Velikiy" reported the sounds of two explosions from the vicinity of the "Kursk", and when the submarine failed to report in as scheduled, search operations began. At 4:30 AM local time, five hours after the search began, and sixteen hours after the submarine had sunk, "Pyotr Velikiy"s sonar detected the wreck of the "Kursk" lying at some from Severomorsk. Rescue operations began, co-ordinated by Admiral Popov aboard the "Pyotr Velikiy". By this time the survivors of the explosion were probably already dead. Kasatonov and the "Pyotr Velikiy" guarded the site of the wreck during rescue and then salvage efforts until October 2000.