In August 2000, the Russian submarine, the Kursk, sank with the loss of 118 lives. It was a tragedy which shocked the world. But to many the tragedy remains incomprehensible, for the Kursk had been built to be unsinkable. How could this submarine have foundered? For a week after the tragedy the world watched in horror, as divers struggled to reach the crew trapped inside the Kursk. But the rescue efforts were in vain - all the sailors on board had perished. One overriding question dominated the aftermath of the disaster: what had caused the submarine to sink? As theories and counter-theories have multiplied, this mystery has been mired in confusion and acrimony. The Russians eventually claimed an American spy submarine had collided with the Kursk, causing her to sink - a claim the Americans flatly deny. But the Russian suspicions were based on logic. During the naval exercises there had indeed been two American submarines out in the Barents Sea, spying on the Russian weaponry and tactics. There is also a long history of collisions between US and Russian submarines in the Barents Sea. And above all, the Russians believed they had found overwhelming evidence showing the Kursk sank as a result of a collision with an American submarine. Satellite photographs and underwater footage all seemed to point to the Russian suspicions being correct. However, new scientific evidence suggests that the Russians were wrong. With access to the very latest scientific research, Horizon tells the story of the alternative theory that shows that it probably wasn't a collision, and may point to the true cause of the tragedy. The disaster left a series of geophysical fingerprints. Through a detailed forensic detective story, seismologists have now been able to establish that the Kursk sank because of an explosion, not a collision. But what had exploded? Horizon follows torpedo designers and chemists as they try to track down the precise cause of the explosion. The scientists'