The Kursk was part of Russia's Northern Fleet, which had suffered funding cutbacks throughout the 1990s. Many of its submarines were tied and rusting in Andreyeva Bay, 100 km from Murmansk. Little work to maintain all but the most essential front-line equipment, including search and rescue equipment, had occurred. Northern Fleet sailors had gone unpaid in the mid-1990s. The end of the decade saw something of a renaissance for the fleet; in 1999, The Kursk carried out a successful reconnaissance mission in the Mediterranean, tracking the US Navy's Sixth Fleet during the Kosovo War. August 2000's training exercise was to have been the largest summer drill – ten years after the Soviet Union's collapse – involving four attack submarines, the fleet's flagship Pyotr Velikiy ("Peter the Great") and a flotilla of smaller ships.

Explosion

The Kursk sailed out to sea to perform an exercise of firing dummy torpedoes at the Pyotr Velikiy, a Kirov class battlecruiser. On August 12, 2000 at 11:28 local time (07:28 UTC), the torpedoes were fired, but soon after there was an explosion on the Kursk. The only credible report to date is that this was due to the failure and explosion of one of the Kursk's new torpedoes. The chemical explosion blasted with the force of 100-250 kg of TNT and registered 2.2 on the Richter scale. The submarine sank to a depth of 108 metres (350 ft), about 135km (85 miles) from Severomorsk, at 69°40′N, 37°35′E. A second explosion 135 seconds after the initial event measured between 3.5 and 4.4 on the Richter scale, equivalent to 3-7 tons of TNT. One of those explosions blew large pieces of debris back through the submarine.

Rescue attempts

Though a rescue attempt was made by British and Norwegian teams, all sailors and officers aboard the Kursk perished. The Russian admiralty at first suggested that most of the crew had died within minutes of the explosion; however, their motivations for making the claim are considered by outside observers as political.

Captain Lieutenant Dimitry Kolesnikov, one of the survivors of the first explosion, survived in Compartment 9 at the aft of the boat for hours after the blasts. Recovery workers found notes on his body. They showed that 23 sailors (out of 118 aboard) had waited in the dark with him.

There has been much debate over how long the sailors might have survived. Some, particularly on the Russian side, say that they would have died very quickly; water is known to leak into a stationary Oscar-II craft through the propeller shafts and at 100 m depth it would have been impossible to plug these. Others point out that the many potassium superoxide chemical cartridges, used to absorb carbon dioxide and chemically release oxygen to enable survival, were found used when the craft was recovered, suggesting that they had survived for several days.

Ironically, these cartridges appear to have been the cause of death; a sailor appears to have accidentally brought a cartridge in contact with the sea water, causing a chemical reaction and a flash fire. The official investigation into the disaster showed that some men appeared to have survived the fire by plunging under the water (the fire marks on the walls indicate the water was at waist level in the lower area at this time). However the fire rapidly used up the remaining oxygen in the air, causing death by asphyxiation.

While the tragedy of the Kursk played out in the Far North, Russia's President Vladimir Putin waited for five days before he broke a holiday at his hideaway in subtropical Sochi on the Black Sea before commenting publicly on the loss of the pride of his Northern Fleet. A year later he said: "I probably should have returned to Moscow, but nothing would have changed. I had the same level of communication both in Sochi and in Moscow, but from a PR point of view I could have demonstrated some special eagerness to return.

Raising

A consortium formed by the Dutch companies Mammoet and Smit International using the barge Giant 4 eventually raised the Kursk and recovered the dead, who were buried in Russia – although three of the bodies were too badly burned to be identified. The heat generated by the first blast detonated the warheads on 5 to 7 torpedoes causing a series of blasts big enough to be measured on geological seismic sensors in the area – and those secondary explosions fatally damaged the vessel.

Russian officials strenuously denied claims that the sub's Granit cruise missiles were carrying nuclear warheads, and no evidence has been provided to the contrary. When a salvage operation raised the boat in 2001, there were considerable fears that moving the wreck could trigger explosions since the bow was cut off in the process using a tungsten carbide-studded cable which had the potential to cause sparks which would ignite remaining pockets of volatile gases, such as hydrogen.

The remains of the Kursk's reactor compartment was towed to Sayda Bay on Russia's northern Kola Peninsula – where more than 50 reactor compartments were afloat at pier points – after a shipyard had defuelled the boat in early 2003. The rest of the boat was then dismantled.