Anti-ship cruise missiles (ASCMs) are modern long-range weapons of naval combat, designed specifically to target ships. Due to their stealth, accuracy, and low-cost, ASCMs have become weapon of choice for militaries around the world. ASCMs were used in over half of attacks on merchant shipping by Iran and Iraq during the Tanker War.[i]
Caption: An Exocet missile fired from a land-based launcher
Iran reportedly has acquired hundreds of ASCMs that they could likely use to try to disrupt oil flows through the Strait.
How ASCMs Work
In order for an ASCM to function properly, it must perform the following sequence correctly:
1) Locate Target with Scanning Radar or Spotters
Some ASCMs locate their targets using radar. This technique requires the launcher to have a line of sight to the target, limiting the range of the missile to the radar horizon and preventing the missile from seeing a target that is hidden by any terrain obstacles. Furthermore, simple scanning radars cannot determine the difference between cargo, container, and oil tanker ships, all of which can be of similar size.
Missiles that locate their targets using scanning radars also emit radio waves, revealing their position. This limits the utility of these missiles in asymmetric warfare: once the launcher reveals its location, it is vulnerable to attack by the adversary's conventional forces.
During the Cold War, the superpowers developed another targeting method, "over-the-horizon targeting," mostly in an effort to expand the range of their missiles. In this technique, a launch technician either programs a missile's flight path or a set of target coordinates, and the missile simply flies to the target area. Over-the-horizon targeting requires a spotter to relay the target coordinates to the shooter, but the shooter need not actually be able to see the target himself. This targeting method has become considerably easier to use in recent years due to the ubiquity of GPS navigation devices.
2) The Missile Must Launch Properly
A booster kit propels the missile from the launch platform to an adequate speed and altitude to enable the missile to transition to the cruise flight mode.
Each type of ASCM uses its own propellant. There are two main types of propellants: 1. liquid; 2. solid. Liquid propellants require complicated piping and pumping equipment to feed their engines and more time to prepare to launch, but they provide greater thrust and an in-flight throttle (although it takes time to build the thrust when first ignited). Solid propellants, on the other hand, do not require complicated engines, but they rely on complicated chemistry during production and on strong casings to withstand the intense pressures that they generate during flight. Solid propellant missiles can fire much faster and accelerate more quickly at liftoff, but they cannot be throttled in flight.
Most modern ASCMs use solid-propellant boosters. The burning rate of the propellant can be affected by temperature, and temperatures higher than 100° F can lead to unsatisfactory performance.[ii] As such high temperatures are commonplace in Iran, this certainly could lead to missile launch problems in an attempt to disrupt traffic in the Strait of Hormuz.
For the cruise phase, ASCMs tend to use ramjet or turbojet engines. Ramjet engines contain no moving parts and compress intake air using the forward speed of the air vehicle. Turbojet engines use a turbine-driven compressor. Both then ignite a mixture of the compressed air and fuel, producing a high-velocity jet in the exhaust plume. The momentum of the exhaust stream then propels the missile forward.[iii]
3) Guide Accurately
Some (especially older) ASCMs use radar to track the position of the target throughout the missile's flight.[iv] This guidance mechanism requires the missile or the launcher to maintain a continuous radar lock on the target, revealing its position and limiting its maneuverability. Losing radar lock would usually cause the missile to miss its target.
More modern missiles that simply follow an internal navigation computer are subject to various kinds of navigation errors. Inertial guidance systems "drift" during flight, which can have a significant impact on accuracy over long distances, but modern inertial navigation systems use updates from GPS receivers or other devices that greatly improve their accuracy.[v] Moreover, within the confines of the Arabian Gulf, drift is unlikely to make a substantial difference. Simple mistakes during entry of the target coordinates or the flight path are a more likely source of error when working with modern weapons.
4) Acquire the Target with the Terminal Guidance
Once an ASCM reaches the vicinity of its target, it turns on its terminal guidance system. Most ASCMs use radar or infra-red seekers, somtimes on multiple bands to circumvent the electronic counter-measures that warship targets typically deploy. The open ocean offers few radar returns or heat signatures in the vicinity of the target ship, so the missile is likely to home in on its intended target. In areas with more ship traffic or near coastlines, terminal guidance systems may choose the wrong target. Radars also sometimes pick up ocean waves or other clutter, leading the missile away from the target ship.
During the Iran-Iraq War, radars incorrectly identified targets as tankers multiple times. For example, Iranians defended tankers loading at their oil terminals by constructing decoys out of ship wreckage and outfitting buoys with radar reflectors. One decoy buoy near Kharg Island was hit approximately 20 times.[vi]
Once a missile hits its target, its warhead must explode to do serious damage, and it turns out that the explosion should not be taken for granted. For example, Exocet missiles frequent failed to explode during the Tanker War and also during the Falklands War (more than 20% of the time). But even if a warhead fails to detonate, the ASCM can still do damage: any remaining fuel in the missile can explode and burn, which could by itself cause significant damage and even a ship loss. During the Falklands War, the HMS Sheffield was hit by an Exocet missile that did not detonate, but the missile's liquid fuel set the destroyer on fire.
The damage caused by the missile will depend on its warhead size. Simply put, larger warheads have more destructive capacity. ASCM warheads range drastically in size, from small 220-pound models to massive 2,200-pound warheads. Although each type of ASCM has its own detailed specifications, missiles produced in eastern states such as Russia and China tend to have larger warheads than western ones.
Relevant Historical Use of ASCMs
Caption: A Mirage aircraft firing an Exocet missile
The maritime threat of ASCMs is serious: ASCMs cause severe damage and are difficult to combat. Historically, ASCMs have played a critical role in warfare.
Iran & ASCMs
Iran currently does not possess any reliable western ASCM. They have either used up these missiles (i.e., Harpoons purchased by the Shah) in Iran-Iraq War, or their Western-supplied systems are so extremely unreliable that they cannot be considered operational (e.g., their Sea Killers).[xi] However, Iran has acquired a number of Chinese ASCM models — perhaps 100 Seersuckers,[xii] 125 Sardines[xiii] and 75 Saccades, and perhaps more.[xiv] There are also reports that Iran acquired the Russian SS-N-22 Moskit, also known as the Sunburn[xv], though the reliability of these reports is disputed.[xvi]
Caption: Sardine / CS 801 missile fired from a naval warship
Caption: Picture of a Moskit (or Sunburn) missile
[i] S. Navias and E.R. Hooton, Tanker Wars: The Assault on Merchant Shipping During the Iran-Iraq Crisis, 1980-1988 (New York: I.B. Taurus & Co Ltd, 1996), pp. 87-88.
[ii] GlobalSecurity.org, SMS GUIDED MISSILES, AERODYNAMICS, AND FLIGHT PRINCIPLES. Online. Available: www.globalsecurity.org/military/library/policy/navy/nrtc/14110_ch9.pdf. Accessed: April 9, 2008.
[iii] MissileThreat.com, Glossary for Cruise Missiles. Online. Available: http://www.missilethreat.com/cruise/pageID.1736/default.asp. Accessed: April 9, 2008
[iv] GlobalSecurity.org, SMS GUIDED MISSILES, AERODYNAMICS, AND FLIGHT PRINCIPLES. Online. Available: www.globalsecurity.org/military/library/policy/navy/nrtc/14110_ch9.pdf. Accessed: April 9, 2008.
[v] David J Nicholls, "Cruise Missiles and Modern War," Occasional Paper No. 13 Center for Strategy and Technology Air War College (May 2000), p. 6.
[vi] Martin S. Navias and E.R. Hooton, Tanker Wars: The Assault on Merchant Shipping During the Iran-Iraq Crisis, 1980-1988 (New York: I.B. Taurus & Co Ltd, 1996), p. XX.
[vii] Carlo Kopp, "Warship Vulnerability," Air Power Australia (July 2005). Online. Available: http://www.ausairpower.net/Warship-Hits.html. Accessed: October 4, 2007
[viii] Carlo Kopp, "Warship Vulnerability," Air Power Australia (July 2005). Online. Available: http://www.ausairpower.net/Warship-Hits.html Accessed: October 4, 2007.
[ix] Christian Lowe ed., "Hezbollah's Surprise Weapons," DefenseTech.org. Online. Available: http://www.defensetech.org/archives/002591.html Accessed: October 4, 2007.
[x] Matt Hilburn, "Asymmetric Strategy: Growing Iranian Navy Relies on ‘Unbalanced Warfare' Tactics,"Navy League of the United States, (December 2006). Online. Available: http://www.navyleague.org/sea_power/dec06-14.php. Accessed: October 4, 2007.
[xi] Anthony Cordesman, Iran's Military Forces in Transition (Westport, Connecticut 1999).
[xii] "C-201 / HY-2 / SY-1 CSS-N-2 / CSS-C-3 / SEERSUCKER," FAS Military Analysis Network. Online. Available: http://www.fas.org/man/dod-101/sys/missile/row/c-201.htm. Accessed: April 9, 2008.
[xiii] E.R. Hooton, ed., Jane's Naval Weapon Systems(Alexandria: Jane's Information Group Inc., 2004), p. 298-300.
[xiv] GlobalSecurity.org, C-802 / YJ-2 / Ying Ji-802 / CSS-C-8 / SACCADEC-8xx / YJ-22 / YJ-82. Online. Available: http://www.globalsecurity.org/military/world/china/c-802.htm. Accessed: April 9, 2008.
[xv] Ariel Cohen, Ph.D., James Phillips, and Wouldiam L. T. Schiran, "Countering Iran's Oil Weapon," Heritage Foundation, (2006).
[xvi] INSS.org, Iran. Online. Available: www.inss.org.il/upload/(FILE)1198577424.pdf. Accessed: April 29, 2008.
[xvii] E.R. Hooton, ed., Jane's Naval Weapon Systems (Alexandria: Jane's Information Group Inc., 2004), pp. 298-300.
[xviii] Anthony Cordesman, Iran's Military Forces in Transition (Westport, Connecticut 1999).
[xix] E.R. Hooton, ed., Jane's Naval Weapon Systems (Alexandria: Jane's Information Group Inc., 2004), pp. 298-300.
[xx] E.R. Hooton, ed., Jane's Naval Weapon Systems (Alexandria: Jane's Information Group Inc., 2004), pp. 295-297.
[xxi] Anthony Cordesman, Iran's Military Forces in Transition (Westport, Connecticut 1999).
[xxii] Thomas G. Mahnken, "The Cruise Missile Challenge," Center for Strategic and Budgetary Assessments, (March 2005).
[xxiii] GlobalSecurity.org, Moskit SS-N-22 Sunburn. Online. Available: www.globalsecurity.org/military/world/russia/moskit.htm. Accessed: April 9, 2008.
This page last modified in August 2008