Ballistic Missile Submarine

Ballistic Missile Submarine, type of submarine specially designed to carry intercontinental (long range) ballistic missiles with nuclear warheads as part of a nation’s nuclear weapons force. There are two types of ballistic missile submarines: the SSBN, which is powered by nuclear energy, and the SSB, which is powered by diesel-electric energy. The initials SSB stand for Ship Submersible Ballistic. Ballistic missile submarines are designed to lurk submerged below the ocean’s surface as a strategic deterrent against nuclear attack by enemies. Modern SSBNs are armed with torpedoes for self-defense but generally rely on their stealth to avoid detection. As a result, SSBNs limit their two-way radio transmissions (which can be picked up by enemy vessels). Instead, SSBNs monitor special low-frequency radio channels. In the event of nuclear war, military leaders would use these channels to send a nuclear missile launch code to the sub. If a launch code were received, several senior officers aboard the submarine would authenticate the order before the launch would take place.

The world’s first ballistic missile submarines were modified Soviet attack submarines, dubbed the Zulu V class by the North American Treaty Organization (NATO). These SSBs appeared in the late 1950s. Each diesel-electric submarine carried two liquid-fueled missiles stored in vertical tubes contained in the sail structure, the part of a submarine that rises above the rest of the hull and contains the periscope and command center. The submarines had to surface and raise the missiles out of the submarine in order to fire, and the missiles had a range of only 520 km (325 mi). Each missile carried a single warhead.

The United States Navy’s first ballistic missile submarines were the nuclear-powered George Washington class, first operational in 1960. They were also modifications of attack submarines, with 16 missile tubes housed in a special compartment in the middle of the submarine. Each tube contained a solid-fuel Polaris missile that could be launched from underwater. Today four of the five major nuclear powers operate significant SSBN forces, including the United States (18 Trident SSBNs with two types of missiles), Russia (two different SSBN types totaling 55 submarines), the United Kingdom (4 submarines), and France (5 submarines). China has only one operational ballistic missile submarine, but has plans for more.

Modern SSBNs share many common characteristics. For instance, they are much larger than attack submarines, because their missiles are encased in vertical launching tubes within the pressure hull. In addition, SSBNs are designed for quietness and stealth rather than maneuverability. The submarine-launched ballistic missiles (SLBMs) carried by modern SSBNs share common features as well. They are all solid-fuel, multistage missiles with intercontinental range. Each SLBM can carry multiple warheads, called MIRVs, which can be aimed at several different targets. Because of their missile range and warhead accuracy, modern SSBNs can operate close to home waters, where defensive antisubmarine warfare forces are close at hand in the event of an attempted enemy attack.

The largest ballistic missile submarines are the U.S. Navy’s Ohio class and the Russian Typhoon missile submarines (originally developed by the former Union of Soviet Socialist Republics). Both have been operational since the early 1980s. The Ohio submarines are 170 m (560 ft) in length and displace 16,830 metric tons of water when submerged. They carry 24 MIRV missiles, either the Trident I (C-4)—which carries eight warheads with a range of 7400 km (4600 mi)—or the improved Trident II (D-5). The Russian Typhoon ballistic missile submarines are 171 m (561 ft) in length and have a submerged displacement of 26,300 metric tons, significantly larger than the Ohio submarines. But each Typhoon has only 20 SS-N-20 ballistic missiles armed with nine warheads apiece, 12 fewer warheads per submarine than the 192 carried by each Trident submarine. The SS-N-20 missile has a flight range of 8300 km (5200 mi).