Strategic missiles represent a logical step in the attempt to attack enemy forces at a distance.
Ballistic missiles are rocket-propelled weapons that travel by momentum in a high, arcing trajectory after they have been launched into flight by a brief burst of power. Cruise missiles, on the other hand, are powered continuously by air-breathing jet engines and are sustained along a low, level flight path by aerodynamic lift.
The modern weapons are generally considered to have their true origins in the V-1 and V-2 missiles launched by Germany in 1944–45.
V2 missiles: The precursor of modern ballistic missiles was the German V-2, a single-stage, fin-stabilized missile propelled by liquid oxygen and ethyl alcohol to a maximum range of about 200 miles.
The first ICBMs ( type of Ballistic missile): In 1957 the Soviets launched a multistage ballistic missile (later given the NATO designation SS-6 Sapwood) as well as the first man-made satellite, Sputnik.
From liquid to solid fuel: This first generation of missiles was typified by its liquid fuel, which required both a propellant and an oxidizer for ignition as well as a complex (and heavy) system of pumps. The early liquid fuels were quite dangerous, difficult to store, and time-consuming to load. The first solid-fueled U.S. system was the Minuteman I. This ICBM, conceived originally as a rail-mobile system, was deployed in silos in 1962, became operational the following year, and was phased out by 1973.
Multiple warheads: By the early 1970s, several technologies were maturing that would produce a new wave of ICBMs. First, thermonuclear warheads, much lighter than the earlier atomic devices, had been incorporated into ICBMs by 1970. Second, the ability to launch larger throw weights, achieved especially by the Soviets, allowed designers to contemplate adding multiple warheads to each ballistic missile. Finally, improved and much lighter electronics translated into more accurate guidance.
The first steps toward incorporating these technologies came with multiple warheads, or multiple reentry vehicles (MRVs), and the Fractional Orbital Bombardment System (FOBS).
The Fractional Orbital Bombardment System (FOBS)
1. A missile is put into a stable orbit around the Earth and deorbits over a target on the Earth.
2. FOBS was based on a low-trajectory launch that would be fired in the opposite direction from the target and would achieve only partial earth orbit. With this method of delivery, it would be quite difficult to determine which target was being threatened. However, given the shallow reentry angles associated with a low trajectory and partial earth orbit, the accuracy of FOBS missiles was questionable.
3. In other words: A Fractional Orbital Bombardment System (FOBS) is a warhead delivery system that uses a low earth orbit towards its target destination. Just before reaching the target, it deorbits through a retrograde engine burn.
4. It had no range limit, its flight path would not reveal the target location, and the maximum altitude would be around 150 km.
Multiple reentry vehicles (MRVs)
A missile carrying MRVs, on the other hand, would be launched toward the target in a high ballistic trajectory. Several warheads from the same missile would strike the same target, increasing the probability of killing that target, or individual warheads would strike separate targets within a very narrow ballistic “footprint.” (The footprint of a missile is that area which is feasible for targeting, given the characteristics of the reentry vehicle.)