Speculation on the causes of the sinking of the Russian submarine Kursk continue. The extensive damage seen in underwater videos is certainly more than could have been caused by a collision, and it is doubtful that even an external weapons hit could cause the huge gaping tear in the pressure hull. Any outside cause of the disaster would have had to penetrate the outer hull and various items (e.g., missiles) before reaching the inner hull. Everything points to an internal explosion. Sound recordings indicate a smaller explosion followed moments later by a larger one. The huge internal explosion wrecked everything back to the control room, and could have incapacitated the crew and watertight doors in the back part of the submarine. With the control room gone, no one could have blown ballast to force the submarine to the surface. The cause of the first internal explosion is unknown but there are two strong candidates. The second explosion, the one that wrecked the submarine, was certainly the detonation of several torpedo warheads. The less likely of the two candidates for the first explosion is that a Shkval underwater rocket was ignited by static electricity and burned. The more likely cause of the first explosion was a leak of torpedo fuel. New Russian torpedoes, which are known to have been on board, use a new mono-propellant which is dangerous and unstable. A leak could have been caused by rough torpedo handling by an inexperienced crew, or by shore-based workers who assembled the torpedo incorrectly. Another possibility is that a torpedo was assembled with plain rubber O-rings instead of the special rings needed to survive contact with the nitrate ester fuel. Once fuel was leaking into the torpedo room, a spark from a dropped tool or from static electricity could have detonated it.--Stephen V Cole