Russia's massive but faulty nuclear subs
The Yekaterinburg nuclear-powered submarine that caught fire while undergoing repairs near Norway's border forms the backbone of Russia's strategic deterrent and is one of its biggest vessels.
The DELTA IV class submarine is among several that can be armed with long-range nuclear weapons that both Moscow and Washington were producing at the height of the Cold War.
Here is a look at some of the submarines still in use today by Russia along with those under development. The data was compiled from Russia's specialized Flot.com navy website and the US-based GlobalSecurity.org watchdog.
The reporting names used by NATO appear in brackets.
-- Project BDR (DELTA III)
Russia lists five of the older-model strategic submarines in its ageing Pacific Fleet near Vladivostok and none in the Northern Fleet in the Murmansk region.
The oldest of the 10,600-tonne craft was commissioned in 1979 and was originally intended to have an operating lifespan of 20 to 25 years.
The Podolsk submarine in this class suffered an on-board explosion in 2004 that killed one sailor. The accident was blamed on a faulty water pressure valve and no other mishaps have been reported on a Russian DELTA III since.
-- Project BDR M (DELTA IV)
The navy's active fleet of six of the more modern versions of the DELTA is entirely based in the Murmansk region.
Ships such as the Yekaterinburg can carry the same 16 long-range nuclear weapons as the DELTA III but descend to lower depths and weigh nearly 1,200 tonnes more.
They are also 12 metres (40 feet) longer and covered with a special rubber coating that helps mute the engine and improves the vessel's stealth capabilities.
It was this coating that reportedly caught fire on board the Yekaterinburg on Thursday when it was undergoing scheduled maintenance work in a shipyard in the military town of Roslyakovo some 100 kilometres (60 miles) east of northern Norway.
-- Project 941 (TYPHOON)
This class of submarines was developed by the Soviet Union alongside the DELTA IV and is codenamed Akula (Shark) in Russian.
These massive 23,200-tonnes submarines do not have to be submerged to fire their strategic weapons and have ice-breaking capabilities.
The craft can fire up to 20 of the next-generation Bulava missiles that have experienced a series of testing failures but which Russia is now incorporating into its rocket forces.
The Murmansk-based Dmitry Donskoi is the only submarine of this type believed to be operated by Russia today. Two other vessels were decommissioned between 2004 and 2010.
-- Project 955
The navy's most recent strategic project is developing what will be known as the fourth-generation Borei class of strategic submarines.
Severe underfunding experienced with the demise of the Soviet Union led to numerous delays following the start of construction in 1996 and none of these vessels are still in operation today.
First to be commissioned is the Yury Dolgoruky -- a 14,720-tonne craft that began undergoing tests in March 2009.
It can carry up to 16 long-range nuclear missiles along with new cruise missiles and has been used in Bulava testing in the past. Two more such submarines are currently under construction.
Russia hopes to complete constructing at least eight such submarines this decade.
-- Kursk (OSCAR II)
The Kursk nuclear submarine suffered the Russian navy's worst-ever disaster when it caught fire and exploded while conducting war games in the Barents Sea in August 2000.
Most of the 118 seamen killed by the accident died instantly but some survived for several days -- with a few keeping heart-breaking diaries written in blood to their loved ones -- before suffocating.
Nuclear-powered submarines such as the Kursk are built to fire shorter-range cruise missiles that may be tipped with nuclear weapons but are primarily used in tactical campaigns.
Nerpa (AKULA II)
The nuclear-powered attack submarine suffered a deadly mishap in the Pacific in its first year of testing in 2008 but is still being leased to India as originally planned.
Twenty sailors died from the accidental release of a dangerous chemical that was mistakenly loaded into the craft's fire extinguishing system.
The 8,140-tonne vessel can fire a range of torpedoes as well as Granat cruise missiles that can be nuclear-tipped. It is due to be commissioned by India after many delays within the coming months.
© 2011 AFP