Torpedo 'own goal' may have triggered explosions

Any explanation for the sinking of the Kursk is speculation based on patchy and conflicting evidence. Among those put forward are a collision of boats or burst ballast tanks. But I believe the cause was an exploding torpedo.

Any explanation for the sinking of the Kursk is speculation based on patchy and conflicting evidence. Among those put forward are a collision of boats or burst ballast tanks. But I believe the cause was an exploding torpedo.

The Kursk and other Oscar II class submarines are known as "carrier-busters", designed to sink US aircraft carriers. One weapon they can use for this purpose is the DST-90 torpedo. The DST-90's propellant includes hydrogen peroxide, a corrosive and unstable substance requiring careful maintenance.

The Kursk was on a torpedo-firing exercise and it is believed that only moments before the explosion she had been given permission to launch one. At 7.30am on 13 August, the torpedo was fired. As it was driven out of the tube by high pressure air, its motor may have ignited leaking fuel, causing the torpedo and warhead to explode just as the missile passed between the inner and outer pressure hulls. This would have been the first blast, equivalent to 200lbs of TNT.

A second explosion equivalent to two tons of TNT followed two minutes later. Perhaps the missile was wedged between the two hulls. With a possible fire in the torpedo room and around high-pressure air systems (such as the ballast tanks) inside the inner hull and between the two hulls, it seems likely that the rising temperature caused other warheads and air systems to explode, tearing the hull apart from the bow to the conning tower. If the crew still had control at this point, they might have tried to surface by blowing the ballast tanks. If the tanks had exploded already, this might explain why the boat lost trim and sank at an angle.

In the face of such vast explosions, almost certainly there would have been casualties. The survival of any men would have depended on the sealing of bulkhead doors in the two-minute gap before the second explosion.

The Kursk is a big boat with a small crew relative to its size. There is a small chance that some men in the stern may have survived behind the water-tight doors and with a relatively large air supply. However, with the overall lack of power and air and with the concussive blast effects, even men in the stern would have been subject to appalling suffering.

Dr Willett is a submarine expert at the Royal United Services Institute, an independent defence think-tank.