In 1965 the U.S. Navy began studies for a missile in the 45 km (25 nm) range class for use against surfaced submarines. The name Harpoon was assigned to the project (i.e. a harpoon to kill "whales", a naval slang term for submarines). The sinking of the Israeli destroyer Eilat in 1967 by a Soviet-built Styx anti-ship missile shocked senior United States Navy officers, who until then had not been conscious of the threat posed by anti-ship missiles. In 1970 Chief of Naval Operations Admiral Elmo Zumwalt accelerated the development of Harpoon as part of his "Project Sixty" initiative, hoping to add much needed striking power to US surface combatants. Harpoon was primarily developed for use on US Navy warships such as the Ticonderoga-class cruiser as their principal anti-ship weapon system.
The Harpoon has also been adapted for carriage on several aircraft, such as the P-3 Orion, the A-6 Intruder, the S-3 Viking, the AV-8B Harrier II, and the F/A-18 Hornet and U.S. Air Force B-52H bombers. Harpoon was purchased by many American allies, including Pakistan, Japan, Singapore, South Korea, Taiwan, the United Arab Emirates and most NATO countries. It has been carried by several U.S. Air Force aircraft, including the B-52H bomber and F-16 Fighting Falcon.
The Royal Australian Air Force is capable of firing AGM-84 series missiles from its F/A-18F Super Hornets, F/A-18A/B Hornets, and AP-3C Orion aircraft, and previously from the now retired F-111C/Gs. The Royal Australian Navy deploys the Harpoon on major surface combatants and in the Collins-class submarines. The Spanish Air Force and the Chilean Navy are also AGM-84D customers, and they deploy the missiles on surface ships, and F/A-18s, F-16s, and P-3 Orion aircraft. The British Royal Navy deploys the Harpoon on several types of surface ship.
The Royal Canadian Navy carries Harpoon missiles on its Halifax-class frigates. The Royal New Zealand Air Force is looking at adding the capability of carrying a stand-off missile, probably Harpoon or AGM-65 Maverick, on its six P-3 Orion patrol planes once they have all been upgraded to P3K2 standard.
The Republic of Singapore Air Force also operates five modified Fokker 50 Maritime Patrol Aircraft (MPA) which are fitted with the sensors needed to fire the Harpoon missile. The Pakistani Navy carries the Harpoon missile on its naval frigates and P-3C Orions. The Turkish Navy carries Harpoons on surface warships and Type 209 submarines. The Turkish Air Force will be armed with the SLAM-ER.
At least 339 Harpoon missiles were sold to the Republic of China Air Force (Taiwan) for its F-16 A/B Block 20 fleet and the Taiwanese Navy, which operates four guided-missile destroyers and eight guided-missile frigates with the capability of carrying the Harpoon, including the eight former U.S. Navy Knox-class frigates and the four former USN Kidd-class destroyers which have been sold to Taiwan. The two Zwaardvis/Hai Lung submarines and 12 P-3C Orion aircraft can also use the missile. The eight Cheng Kung-class frigate, despite being based on the US Oliver Hazard Perry-class class, have Harpoon capabilities deleted from their combat systems, and funding to restore it has so far been denied.
The Block 1 missiles were designated AGM/RGM/UGM-84A in US service and UGM-84B in the UK. Block 1B standard missiles were designated AGM/RGM/UGM-84C, Block 1C missiles were designated AGM/RGM/UGM-84D. Block 1 used a terminal attack mode that included a pop-up to approximately 1800m before diving on the target; Block 1B omitted the terminal pop-up; and Block 1C provided a selectable terminal attack mode.