The first rockets were unguided missiles that had to be aimed at their targets before firing.
The next step was for missiles to stabilize their flight path.
Early strategic ballistic missiles like the German V-2 rocket used in World War II
practiced inertial guidance with gyroscopes to do that.
Modern strategic rocket weapons like ICBMs have supplemented this
with celestial and topographical navigation and also satellite signals.
For smaller, tactical rockets that can be aimed at moving targets, these methods are too inaccurate.
They need aiming and steering mechanisms that can adjust to changes during flight.
Some are remote controlled, i.e. they follow a path that is set out by their launching platform or an observer on the ground.
Both radar and laser beams are used as guidance.
Others have their own built-in homing system to locate their target and move towards it.
Again radar is a common method.
Some rockets home in on the radar signal of their target (passive radar), while others send out radar pulses of their own (active radar).
Light sensors are common in anti-air missiles, mostly infrared.
Advanced missiles have hybrid guiding and homing systems, combining two or even more of the above.
Targets try to mislead guided rockets by various countermeasures.
Radio signals can be jammed; smoke and flares are used to confuse infrared sensors; chaff and again jamming against active radar.
Stealth is a collective term for defense against both active and passive tracking systems.
Since the late 1980's CE aircraft and also ships and land vehicles use light-absorbing materials and angular profiles to absorb and deflect radar beams.
They also minimize their heat exhaustion to evade infrared seekers and use radar sparingly.
Guided missiles are used against vehicles on land, at sea an in the air:
- Anti-tank Missiles (ATM): Unguided anti-tank missiles have been used since World War II. The first guided missile was the British-Australian Malkara, introduced in 1958 CE. Anti-tank missiles have relatively short ranges, from a few hundred meters to a few kilometers. The earliest ones trailed wires behind them to allow an operator to transmit signals to them; this was later replaced by radio. Most modern missiles have high explosive anti-tank warheads. Some are designed to swoop down on tanks from above, where their armor is the weakest.
- Anti-ship missiles: Guided anti-ship missiles appeared as early as the middle of World War II. The Germans were the first to use radio-guided missiles; others followed suit. Anti-ship missiles are usually launched from aircraft or from ships themselves. They have longer ranges than anti-tank missiles, from a few tens of kilometers to a few hundred. As ships are too slow to evade guided missiles, ships have to either avoid detection or try to shoot down attacking missiles.
- Air-to-Surface Missiles (ASM): This category forms a kind of 'precision bombs', aimed at relatively small targets. It partially overlaps with ATMs and anti-ship missiles and here too many are not rockets but cruise missiles. Some home in on enemy radar and thus can be used by aircraft to target enemy air defenses, including SAMs.
- Surface-to-Air Missiles (SAM): During and after World War II, some bombers flew so high that anti-air gunfire had but a slim chance of hitting them. In the early 1950's CE the first SAMs entered service, solving the height problem because they could reach high enough. In the 1960's CE they became so effective that attacking bombers were forced to fly low, ducking under the radar. Today they still are the most effective type of anti-aircraft weapon. Some are heavy, powerful rockets that have ranges up to several hundreds of kilometers. Others are small ones with limited range, but light enough to be carried by a single soldier.
- Air-to-Air Missiles (AAM): These are the equivalent of SAMs, but launched from aircraft themselves. The first AAMs entered service in 1956 CE. Most operate at small or medium range, though some can reach long ranges of a few hundred kilometers. Short range missiles usually rely on infrared sensors to pick up the heat from the exhaust of their target. Medium and long range missiles tend to prefer radar. AAMs often don't hit their target, but explode just next to it, showering it with bomb fragments. Like SAM's, AAMs have become the dominant anti-aircraft weapon, restricting traditional guns to dogfights only.
- Anti-Ballistic Missiles (ABM): Most ABMs are designed to intercept large ICBMs, though some modern ones can counter small and medium range ballistic missiles. Anti-rocket rockets have a difficult job because their targets fly very fast. When ICBMs with multiple warheads were introduced in 1970 CE, the task of ABMs became even harder. In response, their use was restricted in the ABM treaty two years later, though the USA withdrew from it in 2002 CE.
Several guided missiles are not rockets but turbojet / ramjet powered cruise missiles, though in an operational sense its is hard to discern them from their rocket cousins. They share the attributes of guided munitions: long range, speed and especially accuracy. Though guided rockets are much more expensive than traditional guns and 'dumb' bombs, they hit their targets far more often. This is especially important in environments where military targets sit among civilian buildings. Because of this precision, they have all but replaced older types of ammunition. A large part of the modern weapons race is devoted to development of countermeasures to defend against missiles on one side and ways to defeat those countermeasures at the other.