The Harpoon (RGM-84/UGM-84/AGM-84) is a U.S.-designed subsonic antiship cruise missile that has been in service since 1977. Numerous variants have been produced since its inception, including air-, ship-, and sub-launched versions. The Harpoon has also undergone multiple upgrades to improve its range and guidance. Variants of the Harpoon have been exported to 32 countries.¹

Harpoon Development

In 1965 the U.S. Navy began developing an antiship missile designed to target surfaced submarines.

Because the missile would target “whales”—naval slang for submarines—the missile was designated the Harpoon. Following the sinking of the Israeli destroyer Eilat in 1967 by Soviet-made Styx antiship cruise missiles, the U.S. Navy recognized a widening gap in their capabilities and contracted McDonnell-Douglas to begin the Harpoon missile program.²

By 1977, the Navy had deployed the Harpoon as its basic antiship missile for fleet-wide use. An air-launched variant followed soon after, first equipped on the Navy’s P-3 Orion in 1979, and later on F/A-18 Hornet and B-52H Bomber, among other aircraft.³

The air-launched Block 1 E (AGM-84E), known as the Standoff Land Attack Missile (SLAM), enabled the targeting of land-based assets. An extended response SLAM (SLAM-ER) first flew in 1997, doubling the SLAM’s range, as well as introducing Automatic Targeting Acquisition (ATA) technology.⁴ The Harpoon Block II, unveiled in 2009, features autonomous, over-the-horizon range, and can execute both land and air strikes.⁵ Block II+ is currently in development.

Harpoon Variants

Since its introduction in 1977, the Harpoon has received multiple upgrades to its hardware and software, resulting in many variants. For clarity, in 1973 the Navy determined the following designations for the Harpoon family: A= air-launched, R=surface ship-launched, U=underwater-launched, G=surface-attack, M=Guided missile.

Block IA (RGM/UGM/AGM-84A)
Because the air-launched variant (AGM-84A) does not have jettisonable solid propellant boosters, it is shorter and lighter than its surface- and underwater-launched cousins. The AGM-84A is 3.85 m in length and 0.343 m in diameter, with a launch weight of 556 kg, whereas the RGM/UGM-84A measures 4.64 m in length with a diameter of 0.343 m, and a launch weight of 682 kg.⁶

Consequently, the AGM-84A has a longer range of 120 km compared to the RGM/UGM-84A, which has a range of 92.6 km.⁷ For guidance, the Blk IA models rely on inertial navigation for midcourse guidance and active radar during the terminal phase. The missiles are equipped with a 224 kg HE warhead. There are two dedicated launchers for the Harpoon—the Mark 140 Mod-0 and the Mk 141 Mod-1—capable of firing one missile every two seconds. The UGM-84A Encapsulated Harpoon Weapon System (EHWS) is essentially the same as the RGM-84A, except it is launched from submarine torpedo tubes within a launching capsule.⁸

Block IB (RGM/UGM-84C)
Introduced in 1982, this variant presents only slight changes to the flight profile and software of the Block IA. Rather than performing a pop-up maneuver, Blk IB missiles sea-skim toward its target in the terminal phase of flight. Additionally, Blk IB features improved electronic counter countermeasures (ECCM) for increased targeting precision.⁹

Block IC (RGM/UGM-84D)
Introduced in 1985, the Blk IC differs from previous iterations in its flight path, guidance, and targeting technology.

Whereas Blk IB and IA could perform either a low apogee pop-up trajectory or a sea-skimming approach in its terminal phase, the Blk IC can perform both. In addition to improved ECCM performance, Blk IC has a relatively higher altitude in the first part of its flight path to avoid friendly ships and other land masses that may be in the missile’s path. A change in the type of fuel used in the missile increased its range to 124 km.¹⁰

Block ID (RGM84-F)
Introduced in 1991, the Blk ID model improved the range of the missile to 240 km by increasing its length to 5.3 m. The guidance system was changed to allow for earlier descent to sea-skimming altitude, and added re-attack capability in the event a target was lost. However, the model was terminated in 2003 because its length limited the types of launchers capable of firing the missile (both surface and sub launched).¹¹

Block IE (AGM-84E/SLAM)
The SLAM (Standoff Land Attack Missile) uses the Harpoon airframe, warhead, and engine, but largely departs from its predecessors. An air-launched land attack missile, the addition of a Global Positioning System receiver, a Walleye infrared (IIR) optical guidance system, and a Maverick data-link system resulted in a significantly more precise weapon.¹² The missile is 4.5 m in length and 0.34 m in diameter, with a launch weight of 628 kg.¹³ SLAM entered service in 1990 and was successfully employed in Operation Desert Storm and UN relief efforts in Bosnia.¹⁴

Block IG (RGM/UGM-84G)
The Blk IG was developed for vessels equipped with lightweight launchers that were too small for the longer RGM-84F. In other words, the Blk IG takes all the upgrades in the Blk ID model, besides the lengthened fuel tank, and places them in the shorter Blk IC model. Entering service in 1999, the system uses improved software that enables it to navigate up to eight waypoints during flight, and is equipped with automatic shoreline avoidance technology.¹⁵

Block IH (AGM-84K/SLAM-ER)
The SLAM-ER (extended response) first entered service in 1999. The system features an improved IIR seeker, a titanium warhead for greater penetration, and added wings (inspired by the RGM/UGM 109 Tomahawk) to expand the missiles range to 280 km.¹⁶ The missile uses inertial navigation and GPS for midcourse guidance, before switching to its IIR seeker in the terminal phase.¹⁷ Of note, the SLAM-ER uses two-way datalink communication with the AWW-13 Advanced Data Link pod for man-in-the-loop control. SLAM-ER is also the first weapon to feature Automatic Targeting Acquisition technology, enabling the missile to overcome IR countermeasures, better discriminate targets in a cluttered scene, and limit the impact of adverse weather conditions on the missile’s accuracy.¹⁸ The missile is capable of targeting moving ships and moving land targets, with a reported circular error probable of 3 meters.¹⁹

Block II (RGM/UGM-84J/L)
First delivered to the U.S. Navy in 2009, the Blk II combines the inertial measuring unit and software from the Joint Direct Attack Munition and the SLAM-ER’s integrated inertial/GPS guidance.²⁰ These improvements to the missile’s guidance technology allow it to perform in littoral waters. Additionally, the guidance system allows for over-the-horizon targeting via helicopter, enabling targeting of concealed or cluttered targets beyond the radar’s line of sight. The missile carries a 224 kg warhead, and has a circular error probable of 10-13 m.²¹

Block II + ER
Originally introduced in 2015 by Boeing as the Harpoon Next Generation, the Blk II+ Extended Range aims to increase the Blk II’s unclassified range of 124 km. To do so the missile will use a lighter, yet more lethal warhead, and an improved turbojet engine that would double the missile’s range to 248 km.²² In January 2017, Boeing’s director of cruise missile systems said the Blk II+ will be making its final Operational Test shots that year, with initial operational capability planned for mid-year. The Blk II + is set to be deployed on the Navy’s F/A-18 and P-8 Increment III patrol aircraft.²³

Operational History

The Harpoon has been used in combat many times over its nearly 5 decades in service. As part of Operation Morvarid, the Iranian Navy fired three Harpoon missiles against Iraqi vessels. In November 1980 the Iranian missile ship Paykan fired a total of three Harpoon missiles at three Iraqi OSA II fast attack ships. The Harpoons neutralized the targets and allowed Iran to proceed with their operation.²⁴

In March 1986, the U.S. Navy used Harpoon missiles against Libyan forces in the Gulf of Sidra. After U.S. Navy aircraft were attacked by 4 to 6 surface-to-air missiles, the USS Yorktown (DDG-48) fired two Harpoon antiship missiles and several other missiles from an A-6 attack aircraft at two Libyan patrol boats and an S-200 surface-to-air missile site. One of the ships was left burning, dead in the water, while the other was severely damaged.²⁵

On April 18, 1988, the United States sank several Iranian vessels using Harpoons during Operation Praying Mantis. After issuing four separate warnings to the Iranian missile boat Joshan to cease approaching U.S. warships, the USS Wainwright (CG-28) engaged the vessel. The Iranian Joshan launched its own Harpoon missile at the Wainwright, but was thwarted by the Wainwright’s chaff and electronic countermeasures. In response, the Wainwright fired six standard missiles (SM-1’s) and one Harpoon missile. The Joshan was significantly damaged by the attack, and was fully sunk by the Wainwright’s close range guns.²⁶

Another vessel, the Iranian frigate Sahand (F 74), launched shoulder-fired surface-to-air missiles at U.S. aircraft. The aircraft evaded the missiles, and responded by firing two Harpoon missiles, which both found their target. A U.S. frigate, the USS Strauss (DDG-16), also targeted and hit the Sahand with a Harpoon missile, sinking it.²⁷²⁸

Accidents

There have been two accidental launches of the Harpoon system. On July 14, 1981, the USS Coontz (DDG-40) accidentally fired a Harpoon missile that traveled nearly 110 km before presumably crashing in the sea.²⁹

A year later on September 6, 1982 a Danish frigate, the HDMS Peder Skram (F352), accidentally fired a Harpoon missile during manoeuvers that resulted in extensive property damage to over 100 summer cottages but no loss of life.³⁰