Ballistic missile submarine
A ballistic missile submarine is a submarine equipped to launch ballistic missiles at sea, almost always from underwater. They share the engineering challenges of all submarines, but have some unique to their operational role. In general, ballistic missile submarines, all modern versions of which have the naval vessel designation code SSBN (Ship Submersible Ballistic Nuclear), are larger, slower, and quieter than attack submarines.
Ballistic missile submarines are national-level strategic assets; their most important advantage is that they are nearly undetectable, and thus nearly invulnerable. They also must be able to receive orders to fire, or be delegated to do so on their own.
To be undetectable, their designers take extreme care to make them as quiet as possible.
Another major challenge is communicating with submerged submarines. Most radio waves do not penetrate water well, except in the Very Low Frequency or Extremely Low Frequency bands, which require extremely long antennas. Shore stations transmitting on these frequencies are immense, so a survivable approach includes putting them in special-purpose aircraft, such as the E-6 TACAMO.
Yet another challenge is inherent to ballistic missiles, which fly a trajectory calculated to take them from one known point to another known point. Since the submarine is moving, it must have extremely accurate navigation systems to make the point of launch comparably well known as for a land-based intercontinental ballistic missile.
While global navigation satellite systems such as GPS can do this for aircraft and surface ships, they can be only a secondary system to inertial navigation, since GPS signals do not penetrate water. Submarines do occasionally raise antennas as a cross-check on their inertial nativigation systems.
Major powers all experimented, after the Second World War, with submarine-launching of the V-2 missile or derivatives. The cryogenic propellants they used, however, were difficult and dangerous to handle, and, in practice, rockets using them had to be launched on the surface.
For the SSBNs to be an effective deterrent, they also needed nuclear propulsion, so they could stay submerged for their entire patrols. They needed to launch while submerged, or were vulnerable to maritime patrol aircraft.
The Soviet Union began deployments as early as 1955, using a modified land-based missile. The 1959 HOTEL I class was nuclear-propelled, but had to surface to launch.
There has been considerable cooperation between the U.S. and U.K. programs. Both use U.S. missiles, although the nuclear weapons on the U.K. boats are British designed- and built. The United Kingdom currently operates four ballisitic missile submarines, all of which are of the Vanguard-class.
In 1960, the U.S. deployed the first operational submarines that had nuclear propulsion and could launch while submerged. , of the George Washington-class armed with UGM-27 Polaris missiles, in 1960. The program was directed by VADM "Red" Raborn.