The U.S. Navy recently purchased 53 more upgrade kits to turn older Harpoon anti-ship missiles into the latest version; the RGM-84Q-4. This version of Harpoon and has a range of 248 kilometers, an all-weather radar homing guidance system and a new, lighter but more lethal warhead. The 663 kg (1,460 pound) ship launched Harpoon has a 140 kg (308 pound) warhead. It approaches the target low, at about 860 kilometers an hour. GPS gets the missile to the general vicinity of the target, then onboard radar takes over to identify and hit a specific target. This Block II+ version has improved GPS guidance plus a new digital data communications capability that allows for in-flight updates and improved ability to hit a specific target. Block II has an INS (inertial guidance) backup system (in case GPS fails or is jammed) along with several improvements to the software that make it useful against land targets as well as in coastal areas where there are a lot of islands and other geographical clutter.
Harpoon has been around since the 1970s a long history successful combat experience. Each RGM-84Q-4 costs about $1.4 million but the upgrade kits cost $268,000 each and can turn a decade old Harpoon into the latest version. Over 7,500 Harpoons have been built since 1977. The Block II entered service in 2011 and the Block II+ in 2015. So far all Block II+ missiles have been created via upgrade kits which can turn Block 1C Harpoons from the 1990s into the latest version. Harpoons have a shelf life of over a decade and must eventually be refurbished, which usually means replacing the solid fuel rocket motor and other items that degrade over time. Testing has shown that the “remanufactured” missiles are as good as newly built ones, especially the ones fired from ships. The Harpoons carried on aircraft take more of a beating and require refurbishment after a few hundred hours of being carried by aircraft.
In addition to the Harpoon, the navy now has an equally effective missile in the new SM-6 anti-aircraft missile. In 2016 the U.S. Navy successfully modified its new SM-6 (Standard Missile 6) anti-aircraft missile so that it can hit surface ships over 200 kilometers distant. The SM-6 is basically the existing SM-2 anti-aircraft missile with the more capable guidance system of the AMRAAM air-to-air missile, as well as general improvements in the electronics and other components. The SM-6 is a 1.5 ton, 6.55 meter (21.5 foot) long, 533mm (21 inch) diameter missile. It has a max altitude of 33 kilometers (110,000 feet).