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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. An intermediate case is the multiple reentry vehicle (MRV) missile which carries several warheads which are dispersed but not individually aimed. All nuclear-weapon states except Pakistan [lower-alpha 1] and North Korea [lower-alpha 2] are currently confirmed to have deployed MIRV missile systems. Israel is suspected to possess or be in the process of developing MIRVs. [5]
The first true MIRV design was the Minuteman III, first successfully tested in 1968 and introduced into actual use in 1970. [6] [7] [8] The Minuteman III held three smaller W62 warheads, with yields of about 170 kilotons of TNT (710 TJ) each in place of the single 1.2 megatons of TNT (5.0 PJ) W56 used on the Minuteman II. [9] From 1970 to 1975, the United States would remove approximately 550 earlier versions of the Minuteman ICBM in the Strategic Air Command's (SAC) arsenal and replace them with the new Minuteman IIIs outfitted with a MIRV payload, increasing their overall effectiveness. [7] As of 2017 the Minuteman III missile was converted to a single reentry vehicle system. [10] [11] The smaller power of the warheads used (W62, W78 and W87) was offset by increasing the accuracy of the system, allowing it to attack the same hard targets as the larger, less accurate, W56. [9] [12] The MMIII was introduced specifically to address the Soviet construction of an anti-ballistic missile (ABM) system around Moscow; MIRV allowed the US to overwhelm any conceivable ABM system without increasing the size of their own missile fleet. The Soviets responded by adding MIRV to their R-36 design, first with three warheads in 1975, and eventually up to ten in later versions. While the United States phased out the use of MIRVs in ICBMs in 2014 to comply with New START, [13] Russia continues to develop new ICBM designs using the technology. [14]
The introduction of MIRV led to a major change in the strategic balance. Previously, with one warhead per missile, it was conceivable that one could build a defense that used missiles to attack individual warheads. Any increase in missile fleet by the enemy could be countered by a similar increase in interceptors. With MIRV, a single new enemy missile meant that multiple interceptors would have to be built, meaning that it was much less expensive to increase the attack than the defense. This cost-exchange ratio was so heavily biased towards the attacker that the concept of mutual assured destruction became the leading concept in strategic planning and ABM systems were severely limited in the 1972 Anti-Ballistic Missile Treaty in order to avoid a massive arms race.
The military purpose of a MIRV is fourfold:
MIRV land-based ICBMs were considered destabilizing because they tended to put a premium on striking first. [18] The world's first MIRV—US Minuteman III missile of 1970—threatened to rapidly increase the US's deployable nuclear arsenal and thus the possibility that it would have enough bombs to destroy virtually all of the Soviet Union's nuclear weapons and negate any significant retaliation. Later on the US feared the Soviet's MIRVs because Soviet missiles had a greater throw-weight and could thus put more warheads on each missile than the US could. For example, the US MIRVs might have increased their warhead per missile count by a factor of 6 while the Soviets increased theirs by a factor of 10. Furthermore, the US had a much smaller proportion of its nuclear arsenal in ICBMs than the Soviets. Bombers could not be outfitted with MIRVs so their capacity would not be multiplied. Thus the US did not seem to have as much potential for MIRV usage as the Soviets. However, the US had a larger number of submarine-launched ballistic missiles, which could be outfitted with MIRVs, and helped offset the ICBM disadvantage. It is because of their first-strike capability that land-based MIRVs were banned under the START II agreement. START II was ratified by the Russian Duma on 14 April 2000, but Russia withdrew from the treaty in 2002 after the US withdrew from the ABM treaty.
In a MIRV, the main rocket motor (or booster) pushes a "bus" (see illustration) into a free-flight suborbital ballistic flight path. After the boost phase, the bus maneuvers using small on-board rocket motors and a computerized inertial guidance system. It takes up a ballistic trajectory that will deliver a re-entry vehicle containing a warhead to a target and then releases a warhead on that trajectory. It then maneuvers to a different trajectory, releasing another warhead, and repeats the process for all warheads.
The precise technical details are closely guarded military secrets, to hinder any development of enemy counter-measures. The bus's on-board propellant limits the distances between targets of individual warheads to perhaps a few hundred kilometers. [19] Some warheads may use small hypersonic airfoils during the descent to gain additional cross-range distance. Additionally, some buses (e.g. the British Chevaline system) can release decoys to confuse interception devices and radars, such as aluminized balloons or electronic noisemakers.
Accuracy is crucial because doubling the accuracy decreases the needed warhead energy by a factor of four for radiation damage and by a factor of eight for blast damage. Navigation system accuracy and the available geophysical information limits the warhead target accuracy. Some writers believe [ weasel words ] that government-supported geophysical mapping initiatives and ocean satellite altitude systems such as Seasat may have a covert purpose to map mass concentrations and determine local gravity anomalies, in order to improve accuracies of ballistic missiles.[ citation needed ] Accuracy is expressed as circular error probable (CEP). This is the radius of the circle that the warhead has a 50 percent chance of falling into when aimed at the center. CEP is about 90–100 m for the Trident II and Peacekeeper missiles. [20]
A multiple re-entry vehicle (MRV) system for a ballistic missile deploys multiple warheads above a single aimpoint which then drift apart, producing a cluster bomb-like effect. These warheads are not individually targetable. The advantage of an MRV over a single warhead is the increased effectiveness due to the greater coverage; this increases the overall damage produced within the center of the pattern, making it far greater than the damage possible from any single warhead in the MRV cluster; this makes for an efficient area-attack weapon and makes interception by anti-ballistic missiles more challenging due to the number of warheads being deployed at once. [7]
Improved warhead designs allow smaller warheads for a given yield, while better electronics and guidance systems allow greater accuracy. As a result, MIRV technology has proven more attractive than MRV for advanced nations. Multiple-warhead missiles require both a miniaturized physics package and a lower mass re-entry vehicle, both of which are highly advanced technologies. As a result, single-warhead missiles are more attractive for nations with less advanced or less productive nuclear technology. The United States first deployed MRV warheads on the Polaris A-3 SLBM in 1964 on the USS Daniel Webster. The Polaris A-3 missile carried three warheads each having an approximate yield of 200 kilotonnes of TNT (840 TJ). This system was also used by the Royal Navy who also retained MRV with the Chevaline upgrade, though the number of warheads in Chevaline was reduced to two due to the ABM counter-measures carried. [7] The Soviet Union deployed 3 MRVs on the R-27U SLBM and 3 MRVs on the R-36P ICBM. Refer to atmospheric re-entry for more details.
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An intercontinental ballistic missile (ICBM) is a ballistic missile with a range greater than 5,500 kilometres (3,400 mi), primarily designed for nuclear weapons delivery. 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 vehicle (MIRVs), allowing a single missile to carry several warheads, each of which can strike a different target. The United States, Russia, China, France, India, the United Kingdom, Israel, and North Korea are the only countries known to have operational ICBMs.
The UGM-73 Poseidon missile was the second US Navy nuclear-armed submarine-launched ballistic missile (SLBM) system, powered by a two-stage solid-fuel rocket. It succeeded the UGM-27 Polaris beginning in 1972, bringing major advances in warheads and accuracy. It was followed by Trident I in 1979, and Trident II in 1990.
In nuclear strategy, a first strike or preemptive strike is a preemptive surprise attack employing overwhelming force. First strike capability is a country's ability to defeat another nuclear power by destroying its arsenal to the point where the attacking country can survive the weakened retaliation while the opposing side is left unable to continue war. The preferred methodology is to attack the opponent's strategic nuclear weapon facilities, command and control sites, and storage depots first. The strategy is called counterforce.
The LGM-30 Minuteman is an American land-based intercontinental ballistic missile (ICBM) in service with the Air Force Global Strike Command. As of 2024, the LGM-30G 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 II submarine-launched ballistic missile (SLBM) and nuclear weapons carried by long-range strategic bombers.
The LGM-118 Peacekeeper, originally known as the MX for "Missile, Experimental", was a MIRV-capable intercontinental ballistic missile (ICBM) produced and deployed by the United States from 1985 to 2005. The missile could carry up to twelve Mark 21 reentry vehicles, each armed with a 300-kiloton W87 warhead. Initial plans called for building and deploying 100 MX ICBMs, but budgetary concerns limited the final procurement; only 50 entered service. Disarmament treaties signed after the Peacekeeper's development led to its withdrawal from service in 2005.
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.
The UGM-133A Trident II, or Trident D5 is a submarine-launched ballistic missile (SLBM), built by Lockheed Martin Space in Sunnyvale, California, and deployed with the United States and Royal Navy. It was first deployed in March 1990, and remains in service. The Trident II Strategic Weapons System is an improved SLBM with greater accuracy, payload, and range than the earlier Trident C-4. It is a key element of the U.S. strategic nuclear triad and strengthens U.S. strategic deterrence. The Trident II is considered to be a durable sea-based system capable of engaging many targets. It has payload flexibility that can accommodate various treaty requirements, such as New START. The Trident II's increased payload allows nuclear deterrence to be accomplished with fewer submarines, and its high accuracy—approaching that of land-based missiles—enables it to be used as a first strike weapon.
The R-36 is a family of intercontinental ballistic missiles (ICBMs) and space launch vehicles (Tsyklon) designed by the Soviet Union during the Cold War. The original R-36 was deployed under the GRAU index 8K67 and was given the NATO reporting name SS-9 Scarp. It was able to carry three warheads and was the first Soviet MRV missile. The later version, the R-36M, also known as RS20, was produced under the GRAU designations 15A14 and 15A18 and was given the NATO reporting name SS-18 Satan. This missile was viewed by certain United States analysts as giving the Soviet Union first strike advantage over the U.S., particularly because of its rapid silo-reload ability, very heavy throw weight and extremely large number of re-entry vehicles. Some versions of the R-36M were deployed with 10 warheads and up to 40 penetration aids and the missile's high throw-weight made it theoretically capable of carrying more warheads or penetration aids. Contemporary U.S. missiles, such as the Minuteman III, carried up to three warheads at most.
The RT-2PM Topol was a mobile intercontinental ballistic missile designed in the Soviet Union and in service with Russia's Strategic Missile Troops. As of 2014, Russia planned to replace all RT-2PM ICBMs with versions of Topol-M. In December 2023, the last Topol regiment was taken off combat duty.
The maneuverable reentry vehicle is a type of warhead for ballistic missiles that is capable of maneuvering and changing its trajectory.
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The W71 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 W62 was an American thermonuclear warhead designed in the 1960s and manufactured from March 1970 to June 1976. Used on some Minuteman III ICBMs, it was partially replaced by the W78 starting in December 1979, and fully replaced by W87 warheads removed from MX Peacekeeper missiles and retired in 2010.
A nuclear triad is a three-pronged military force structure of land-based intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and strategic bombers with nuclear bombs and missiles. Countries build nuclear triads to eliminate an enemy's ability to destroy a nation's nuclear forces in a first-strike attack, which preserves their own ability to launch a second strike and therefore increases their nuclear deterrence.
A penetration aid is a device or tactic used to increase an aircraft's capability of reaching its target without detection, and in particular intercontinental ballistic missile (ICBM) warhead's chances of penetrating a target's defenses.
Agni-V is a land based nuclear MIRV-capable Intercontinental Ballistic Missile (ICBM) developed by the Defence Research and Development Organisation (DRDO) of India. The missile has a range of more than 7,000 km. It is a three-stage, road-mobile, canisterised and solid-fueled ballistic missile.
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.
Agni-VI(Sanskrit: अग्नि; IAST: Agni; lit. Fire) is an MIRV-capable intercontinental ballistic missile under development by the Defence Research and Development Organisation (DRDO) for the Strategic Forces Command (SFC) of the Indian Armed Forces.
The idea of multiple warheads dates back to the mid-1960s, but the key year in the history of the MIRV concept was 1962 when several of technological developments made it possible for scientists and engineers to conceive of multiple, separately targeted warheads that could hit a growing list of Soviet nuclear threat targets. One important innovation was that the weapons laboratories had designed small thermonuclear weapons, a necessary condition for deploying multiple reentry vehicles on the relatively small Minuteman.