In anti-ballistic missile (ABM) defence the cost-exchange ratio is the ratio of the incremental cost to the aggressor of getting one additional warhead through the defence screen, divided by the incremental cost to the defender of offsetting the additional missile. For instance, a single new ICBM might require a single new ABM to counter it, and if they both cost the same, the cost-exchange ratio would be 1:1.
Throughout the Cold War, the cost-exchange ratio was almost always strongly in favor of the offense. Some of this has to do with the fact that an ICBM can be aimed at any target, which the defender cannot know in advance. To shoot that warhead down, the defender has to wait until it appears on radar, which typically happens only a few hundred miles from the target. This means a single defensive missile cannot be used to counter a single warhead; ABMs have to be deployed in a spread-out fashion so that one can respond no matter where the warhead appears. Even if a single ABM is needed to shoot down that single new missile, that single new ABM would be needed to be added to multiple bases depending on their range. For short-range weapons like the Sprint, dozens are needed for every new Soviet warhead.
Through the 1950s and 60s there were intense ongoing debates about the exact figures of the cost-exchange ratio. This ended with the introduction of multiple independently targetable re-entry vehicles, or MIRVs. MIRV allowed a single ICBM to launch multiple warheads, each attacking a different target. Now every new ICBM required dozens and dozens of new ABMs to counter it, swinging the cost-exchange ratio so dramatically in favor of the offense that it ended any debate on the topic. Consideration of cost-exchange ratios was influential in persuading the United States and the Soviet Union to sign the ABM Treaty.
The topic was once again a consideration in the era of the Strategic Defense Initiative, SDI or "Star Wars". In this case the defensive weapons attacked the ICBMs before they released their warheads, reducing the exchange ratio to one, although at a very high dollar cost. Some weapons, like the Project Excalibur system, completely reversed the ratio by attacking dozens of missiles at once, a single weapon thereby potentially destroying hundreds of warheads. Ultimately these technologies failed to mature and the system was ultimately abandoned with the ending of the Cold War.
An anti-ballistic missile (ABM) is a surface-to-air missile designed to counter ballistic missiles. Ballistic missiles are used to deliver nuclear, chemical, biological, or conventional warheads in a ballistic flight trajectory. The term "anti-ballistic missile" is a generic term conveying a system designed to intercept and destroy any type of ballistic threat; however, it is commonly used for systems specifically designed to counter intercontinental ballistic missiles (ICBMs).
The Anti-Ballistic Missile Treaty (1972—2002) was an arms control treaty between the United States and the Soviet Union on the limitation of the anti-ballistic missile (ABM) systems used in defending areas against ballistic missile-delivered nuclear weapons. Under the terms of the treaty, each party was limited to two ABM complexes, each of which was to be limited to 100 anti-ballistic missiles.
An intercontinental ballistic missile (ICBM) is a missile with a minimum range of 5,500 kilometres (3,400 mi) primarily designed for nuclear weapons delivery. Similarly, conventional, chemical, and biological weapons can also be delivered with varying effectiveness, but have never been deployed on ICBMs. Most modern designs support multiple independently targetable reentry vehicles (MIRVs), allowing a single missile to carry several warheads, each of which can strike a different target. India, Russia, the United States, North Korea, China, the United Kingdom and France are the only countries that have ICBMs.
The LGM-30 Minuteman is an American land-based intercontinental ballistic missile (ICBM) in service with the Air Force Global Strike Command. As of 2021, the LGM-30G Minuteman III version is the only land-based ICBM in service in the United States and represents the land leg of the U.S. nuclear triad, along with the Trident submarine-launched ballistic missile (SLBM) and nuclear weapons carried by long-range strategic bombers.
A multiple independently targetable reentry vehicle (MIRV) is an exoatmospheric ballistic missile payload containing several warheads, each capable of being aimed to hit a different target. The concept is almost invariably associated with intercontinental ballistic missiles carrying thermonuclear warheads, even if not strictly being limited to them. By contrast, a unitary warhead is a single warhead on a single missile. An intermediate case is the multiple reentry vehicle (MRV) missile which carries several warheads which are dispersed but not individually aimed. Only the United States, the United Kingdom, France, Russia and China are currently confirmed to possess functional MIRV missile systems. Pakistan and India are developing MIRV missile systems. Israel is suspected to possess or be in the process of developing MIRVs.
Chevaline was a system to improve the penetrability of the warheads used by the British Polaris nuclear weapons system. Devised as an answer to the improved Soviet anti-ballistic missile defences around Moscow, the system increased the probability that at least one warhead would penetrate Moscow's anti-ballistic missile (ABM) defences, something which the Royal Navy's earlier UGM-27 Polaris re-entry vehicles (RV)s were thought to be unlikely to do.
National missile defense (NMD) is a generic term for a type of missile defense intended to shield an entire country against incoming missiles, such as intercontinental ballistic missile (ICBMs) or other ballistic missiles.
START II was a bilateral treaty between the United States and Russia on the Reduction and Limitation of Strategic Offensive Arms. It was signed by US President George H. W. Bush and Russian President Boris Yeltsin on 3 January 1993, banning the use of multiple independently targetable re-entry vehicles (MIRVs) on intercontinental ballistic missiles (ICBMs). Hence, it is often cited as the De-MIRV-ing Agreement. Despite negotiations, it never entered into effect. It was ratified by the US Senate on 26 January 1996 with a vote of 87–4. Although Russia ratified START II on 14 April 2000, it withdrew from the treaty on 14 June 2002 in response to US withdrawal from the ABM Treaty.
Missile defense is a system, weapon, or technology involved in the detection, tracking, interception, and destruction of attacking missiles. Conceived as a defense against nuclear-armed intercontinental ballistic missiles (ICBMs), its application has broadened to include shorter-ranged non-nuclear tactical and theater missiles.
The Safeguard Program was a U.S. Army anti-ballistic missile (ABM) system designed to protect the U.S. Air Force's Minuteman ICBM silos from attack, thus preserving the US's nuclear deterrent fleet. It was intended primarily to protect against the very small Chinese ICBM fleet, limited Soviet attacks and various other limited-launch scenarios. A full-scale attack by the Soviets would easily overwhelm it. It was designed to allow gradual upgrades to provide similar lightweight coverage over the entire United States over time.
Nuclear weapons delivery is the technology and systems used to place a nuclear weapon at the position of detonation, on or near its target. Several methods have been developed to carry out this task.
The W-71 nuclear warhead was a US thermonuclear warhead developed at Lawrence Livermore National Laboratory in California and deployed on the LIM-49A Spartan missile, a component of the Safeguard Program, an anti-ballistic missile (ABM) defense system briefly deployed by the US in the 1970s.
The Parallel Element Processing Ensemble (PEPE) was one of the very early parallel computing systems. Bell began researching the concept in the mid-1960s as a way to provide high-performance computing support for the needs of anti-ballistic missile (ABM) systems. The goal was to build a computer system that could simultaneously track hundreds of incoming ballistic missile warheads. A single PEPE system was built by Burroughs Corporation in the 1970s, by which time the US Army's ABM efforts were winding down. The design later evolved into the Burroughs Scientific Computer for commercial sales, but a lack of sales prospects led to it being withdrawn from the market.
Anti-ballistic missile defense countermeasures are tactical or strategic actions taken by an attacker to overwhelm, destroy, or evade anti-ballistic missile defenses.
A nuclear triad is a three-pronged military force structure that consists of land-launched nuclear missiles, nuclear-missile-armed submarines, and strategic aircraft with nuclear bombs and missiles. Specifically, these components are land-based intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and strategic bombers. The purpose of having this three-branched nuclear capability is to significantly reduce the possibility that an enemy could destroy all of a nation's nuclear forces in a first-strike attack. This, in turn, ensures a credible threat of a second strike, and thus increases a nation's nuclear deterrence.
A penetration aid is a device or tactic used to increase an intercontinental ballistic missile (ICBM) warhead's chances of penetrating a target's defenses.
In nuclear strategy, a counterforce target is one that has a military value, such as a launch silo for intercontinental ballistic missiles, an airbase at which nuclear-armed bombers are stationed, a homeport for ballistic missile submarines, or a command and control installation.
Nike Zeus was an anti-ballistic missile (ABM) system developed by the US Army during the late 1950s and early 1960s that was designed to destroy incoming Soviet intercontinental ballistic missile warheads before they could hit their targets. It was designed by Bell Labs' Nike team, and was initially based on the earlier Nike Hercules anti-aircraft missile. The original, Zeus A, was designed to intercept warheads in the upper atmosphere, mounting a 25 kiloton W31 nuclear warhead. During development, the concept changed to protect a much larger area and intercept the warheads at higher altitudes. This required the missile to be greatly enlarged into the totally new design, Zeus B, given the tri-service identifier XLIM-49, mounting a 400 kiloton W50 warhead. In several successful tests, the B model proved itself able to intercept warheads, and even satellites.
Sentry, known for most of its lifetime as LoADS for Low Altitude Defense System, was a short-range anti-ballistic missile (ABM) design made by the US Army during the 1970s. It was proposed as a defensive weapon that would be used in concert with the MX missile, a US Air Force ICBM that was under development.
Prim–Read theory, or Prim–Read defense, was an important development in game theory that led to radical changes in the United States' views on the value of anti-ballistic missile (ABM) systems. The theory assigns a certain cost to deploying defensive missiles and suggests a way to maximize their value in terms of the amount of damage they could reduce. By comparing the cost of various deployments, one can determine the relative amount of money needed to provide a defense against a certain number of ICBMs.