The ballistic missile submarine or SSBN¹, is without doubt the most powerful weapon ever built, and, consequently, one of the most controversial. Its sole purpose is to maintain the operating nation's nuclear deterrent. It is an oft-quoted factoid that one submarine can carry more firepower than every single bomb dropped in both World Wars put together, including the two atomic bombs.

At a time when every man and his dog are acquiring nuclear weapons, it is perhaps slightly comforting to learn that only five countries are capable of delivering those weapons anywhere in the world at a moment's notice from a hidden location. Only the US, Russia, UK, France and China operate SSBNs, and there are currently less than 40 in service globally - of which less than half would be actively on patrol. This is in part due to their massive cost² – apart from the obvious technical problems of building a mobile platform capable of both launching multiple space vehicles at zero notice and staying underwater for months, their designers have to address the huge safety implications of carrying both a nuclear reactor and multiple nuclear weapons. The possible consequences of an error are unthinkable, so despite what Hollywood may have you believe, as much risk as is humanly possible must be designed out at the start.

Background

The German World War II V-2 rocket is widely regarded as the first ballistic missile. It was powered by a rocket motor which would carry it about 200 miles before the fuel ran out, after which it would drop like a stone onto an essentially random area of the UK. It was very effective: it could be fired from friendly territory without risking a manned aircraft for delivery, and could reach speeds of 3,500mph, making it extremely difficult to shoot down.

The potential was not lost on the allies. Immediately following World War II, the USSR, US and UK all embarked on strategic missile programmes using data, expertise and equipment liberated from the Germans. The US and USSR in particular entered their now infamous arms race, building progressively larger and more powerful missiles, capable of reaching more distant targets. The competition effectively reached stalemate with the commissioning of the first ICBMs³. The Soviets were slightly ahead and the first live test of a Soviet R-7 ICBM was detected in August 1957, closely followed by the launch of Sputnik 1 in October, also on top of an R-7. The US mainland was suddenly under immediate threat. The US responded in the same year with their first ICBM, the Atlas, also used in the Mercury manned space programme.

In the following years, the US and the USSR developed a 'triad' approach to their nuclear deterrents, with ground-launched ICBMs housed in underground silos or on road or rail trucks, aircraft-carrying bombs or shorter-range missiles and Submarine-Launched Ballistic Missiles (SLBMs). This three-pronged approach was intended to ensure that no pre-emptive attack could disable or destroy their entire nuclear capability, so the aggressor's destruction would be assured. The advantages of the submarine deterrent were obvious; the main one being that it could be hidden nearly anywhere in the world for several months.

Unsurprisingly, opposing nations make inordinate efforts to track these boats. When a ballistic missile boat leaves port you can be sure that the event is being watched – probably by satellite, a few ground-based observers and more than likely a couple of submarines lurking and waiting to follow it to sea. In fact, one of the main roles of an attack submarine (SSN) today is to stalk SSBNs and sink them before they have a chance to launch in the event that hostilities break out. Subsequently, SSBNs often have their own SSN escort to ensure that it is not being tracked. And so on...

The Platform

Ballistic missile submarines all share some key characteristics. They are all nuclear-powered - this enables them to stay submerged for months at a time. A conventionally-powered submarine would have to surface for air frequently, thus risking detection. The reactor heats water to produce steam, which then drives steam turbines to turn one or two large propellers or propulsors. The larger the propeller, the slower it needs to rotate and so the quieter it will be. The steam also drives steam generators which provide electrical power. As long as the boat has power, it can produce fresh water and oxygen from seawater; the only limit to its endurance is the amount of food it can carry for the crew.

They are all much larger than their non-missile carrying fleet or attack submarines, although SSBNs tend to have similar sensors, command and control and conventional weapons as attack submarines. All carry torpedoes for self-defence and some also carry anti-ship missiles such as Exocet or Sub-Harpoon. Russian boats also carry surface-to-air missiles that can be used when surfaced. Despite their size, they are also extremely quiet – it would make no sense to spend billions on development and then skimp on detectability.

The Missiles

The missiles themselves are generally just very thin metal tubes containing a huge quantity of solid or liquid fuel and oxidiser, usually in multiple stages and topped with a small guidance system and the warhead itself. All are launched while submerged, by pressurising the launch tube with gas. The missile's engines ignite after it has cleared the surface of the water, boosting it above the atmosphere where the warhead is released to fall back to earth.

The warheads are generally of 100kt⁴ yield or less, much smaller than the massive Megatonne-plus thermonuclear bombs tested during the Cold War. This enables each missile to carry several of them, and also makes them harder to intercept. Nearly all SLBMs carry a number of Multiple Independently-targetable Re-entry Vehicles, MIRVs, meaning that a single missile can destroy several separate targets, although being ballistic weapons all the targets have to be in the same general area. The targeting accuracy is measured by the Circle of Equal Probability (CEP), the radius of the circle within which half the strikes will impact. Considering that the warheads are merely dropped from space, they can be surprisingly accurate - less than 150m in the case of Trident.

SSBNs by Country

Russia

In 1991, when the START 1 treaty was signed, the USSR had no less than 62 operational SSBNs. Following the collapse of the USSR, this number has plummeted to around ten. Accelerating inflation and an overall decline of some 40-60% in gross national product have resulted in serious funding shortages for the armed forces. Between 1990 and 1995, navy manning levels were cut by 50 per cent. Many ships are now laid up in dock, and essential maintenance is no longer being carried out. There have also been a number of highly-publicised accidents, some resulting in multiple deaths and some only narrowly avoiding the release of radioactive material. It is likely that some of the few remaining SSBNs are not fully operational or seaworthy, but even in their semi-retired state they still constitute a serious threat.

The first Soviet ballistic missile submarine was an adaptation of a 611 (Zulu) class diesel-powered boat (SSB), designated B-611. The first of class, B-62, was completed in 1955 and carried a single R-11FM (Scud) missile. The first nuclear-powered boat was the 658 (Hotel) class built in 1960, entering service at around the same time as the 629 (Golf) class SSB. There followed the 667A (Yankee) series and of 1964 onwards and 667B (Delta) series still in use today. The current fleet is as follows:

Project 941, Akula (Shark) (NATO designation Typhoon⁵) - the Typhoon is the largest submarine ever built, and at 48,000 tonnes submerged displacement is bigger than some aircraft carriers. It was designed both for long endurance and under-ice operation, and is capable of breaking through ice to launch if required. It is unusual in its construction, having two parallel pressure hulls and two reactors. It is also notable among submariners for housing saunas and a swimming pool⁶. It has a crew of 160, length of 172m, span of 23m and can dive to 500m and reach speeds of 27knots. Of the six made, only two remain in active service, and as the SS-N-20 missiles are nearing the end of their useful life, with no replacement, it is likely that the Typhoons will be retired along with them.

Weapons – the Typhoon carries 20 RSM-52 three-stage solid fuel missiles (NATO designation SS-N-20 Sturgeon), with 8,300km range and each weighing 84 tonnes. Each missile carries ten 100kt MIRVs. The sub also carries the SS-N-15 Starfish 200kt nuclear anti-ship missile.

Project 667BDRM, Delfin (Dolphin) (NATO designation Delta IV): there are seven of these in service. Displacement (submerged) is 18,000 tonnes, crew 135, length 167m.

Weapons – 16 RSM-54 missiles (NATO designation SS-N-23 Skiff): These are three-stage liquid-fuel missiles with a range of 8,300km. The warhead consists of four MIRVs, each rated at 100kt. Like the Typhoon, Delta-IVs also carry Starfish missiles.

Project 667BDR, Kalmar (Squid) (NATO designation Delta III): 14 boats were commissioned and six are still believed to be capable of launching, although their seaworthiness in uncertain. Displacement (submerged) – 10,600 tonnes, crew 130, length 155m.

Weapons: 16 RSM-50 missiles carrying three warheads each. Project 955, or Borey, is the Russian Navy's intended replacement for Typhoon and Delta IVs. 12 or 16 were planned and the first keel (Yuri Dolgoruky) was laid in 1996. Details are sketchy, but each submarine is expected to carry 12 Bulava SLBMs with four or six warheads each.

United States

The first true Submarine-Launched Ballistic Missile (SLBM) was the US Polaris, carried by the first true SSBN, the USS George Washington, in 1960. The Washington was the first of five boats, and the last to be decommissioned in 1985. The second of class, USS Patrick Henry was controversially based at the Holy Loch in Scotland.

The Ethan Allen class entered service in 1962 just after Washington, and also carried 16 Polaris missiles. The first and only US live nuclear-armed SLBM launch was from Ethan Allen on 6 May, 1962. Again, there were five boats, the last of which was decommissioned in 1991. The 19-ship strong Lafayette class followed, ultimately carrying Poseidon missiles in place of Polaris, and remained in service from 1962 to 1995. The 12 boats of the Benjamin Franklin class followed Lafayette and were based on a similar design; again the last boats were retired in 1995 and replaced by the current Ohio class.

Ohio – there are 18 boats in the class⁷, although under the requirements of the Strategic Arms Reduction Treaty, START II, which was agreed in June 1992, the number of strategic missile submarines was limited to 14 from the year 2002. Rather than decommissioning these four submarines, the US Navy is converting them to SSGNs (Ship, Submersible, Guided Missile, Nuclear) – conventional guided missile) carrying mainly Tomahawk Land-Attack Missiles (TLAM). Each boat has a submerged displacement of 19,000 tonnes, is 171m long and has a crew of 155.

Weapons – 24 Trident D5 3-stage solid fuel missiles. Each is 13.4m tall and weighs 59 tonnes. Range is between 7,360km and 12,000km, depending on the payload. Each missile can carry up to 12 100kt MIRVs, but again treaties limit the number to eight.

United Kingdom

ResolutionThe UK's submarine nuclear force entered service in 1968 when HMS Resolution went on patrol for the first time. There were ultimately four boats in the class, of 7,500 tonnes each, and loosely based on the earlier Valiant-class SSN but adapted to carry US-made Polaris missiles. These were not fully replaced until the last Vanguard-class boat, Vengeance, entered service in 1999.

Vanguard – there are also four of these, HMS Vanguard, Victorious, Vigilant and Vengeance, to ensure one is on patrol at any one time. This single submarine carries the UK's entire active nuclear arsenal. Each vessel will routinely carry a maximum of 48 warheads, although in a crises up to three submarines could put to sea, fielding a total 144 warheads. Each boat is 15,900 tonnes, 150m long and needs a crew of 135.

Weapons – the boat carries 16 Trident D5 missiles supplied by the US; the UK however manufactures its own warheads. Each missile can technically carry up to 12 MIRVs of up to 120kt yield each, but START II agreements limit this to eight, and the UK's 1998 Strategic Defence Review limit the number carried per sub to 48. As can be seen, the number of warheads actually carried is considerably less than the maximum possible; it is therefore likely that a mix of missile capabilities would be fitted to a single submarine, enabling a considerably reduced or 'sub-strategic' response against a single target if required. This flexibility is further enhanced by the ability to selectively control the yield of each warhead.

France

Le Redoutable became France's first ballistic sub when she entered service in 1971. Six boats were built altogether. Four of these underwent major overhauls in the 1980s and became known as the L'Inflexible class following the decommissioning of Le Redoutable in 1991, after the first boat to receive the upgrade. Despite the expense of these upgrades, all have now been decommissioned except for L'Inflexible herself, which will stay in service until replaced by the Le Terrible in 2010.

Le Triomphant – in line with UK strategy, there will ultimately be four of these, Le Triomphant, Le Temeraire, Le Vigilant and Le Terrible. Submerged displacement is 14,300 tonnes, crew size is 111 and length is 138m. Unlike the UK, France maintains an airborne nuclear capability in the form of the ASMP (Air-Sol Moyenne Portee) cruise missile carried by Mirage and Rafale aircraft. This is however a short-range tactical weapon rather than a strategic deterrent.

Weapons - 16 MSBS M45 three-stage solid fuel ballistic missiles with a range of 6,000km, each armed with six TN-75 MIRV warheads of 100kt each. The M45 will be replaced by the more capable M51 SLBM, beginning in 2010. The new missile will have an increased range and new warhead, and all in-service boats will be upgraded to carry it.

China

China is believed to have a substantial tactical and medium range nuclear capability based mainly around air-launched and ground-launched missiles. These missiles are capable of hitting China's immediate neighbours and most of Russia, but not the US. Given its status as the most populous country in the world, the second biggest economy and a past and aspiring superpower, it is widely believed that it will pursue the capability to strike at the US.

Not a great deal is known about China's naval nuclear capabilities, or at least not much is in the public domain. It is known that a single ballistic missile submarine, the Xia, entered service in 1988 and was reportedly followed by a second of class, although the latter boat is no longer in service for reasons unknown. At 6,500 tonnes, the Xia is smaller than most of its contemporaries and, although nuclear-powered, is believed to be limited in operating range. The Xia carried 12 Julang-1 (NATO designation CSS-N-3) two-stage solid fuel missiles, each with a single 250kT warhead.

It is also known that a successor to the Xia, Project 094, has been under development for some time. It is expected that there will be four to six ships, with the first being commissioned in 2008/10. These will be armed with 16 Julang-2 three-stage SLBMs, and it is expected that the submarine/missile combination will enable China to hit any location inside US territory.