The Air Force has been chalking up kills the past two weeks as its fighter jets shot down a Chinese spy balloon followed by a series of unidentified flying objects over the United States. But no matter whether the F-22 or the F-16 fired it, the missile taking down all these mysterious visitors has been the same: the AIM-9X Sidewinder. 

The AIM-9 is a family of heat-seeking, air-to-air missiles that have an estimated 270 aircraft kills to their name, according to a 2004 Air Force press release. Though there are several variants of the missile, it generally weighs about 190 pounds, is approximately 9 feet long, and has a diameter of about 5 inches, according to the weapon’s fact sheet. The AIM-9X is the latest iteration of the AIM-9 and can be fired from most U.S. military fighter jets, including the F-15, the F/A-18, F-35 and, as proven by recent events, the F-22 and F-16

aim-9x sidewinder
An AIM-9X Sidewinder missile shoots off the rail of an F-16 flown by Capt. Spencer “Memphis” Bell, over the test range at Holloman Air Force Base, New Mexico, Apr. 24, 2019 (Tech. Sgt. John Raven/U.S. Air Force)

The Sidewinder dates all the way back to the first successful test firing of the AIM-9A prototype in September 1953. In the years leading up to that, many U.S. military planners were focused on developing radar-guided missiles that could hit large Soviet bombers from as far away as possible. But a team of engineers led by Dr. William McLean at Naval Ordnance Test Station China Lake, California tried their hands at developing a more nimble weapon that could help fighters strike a wider range of targets and close the performance gap between the Navy’s primary fighter, the F9F Panther, and its Eastern Bloc opponent, the MiG-15.

The AIM-9 was relatively cheap to develop, partly because it was built with many “off-the-shelf” parts that already existed, explained military historian James Young in a 2021 history of the Sidewinder.

“Taken together, these factors meant the Navy’s ideal missile might be a cheap, easy-to-use weapon that both markedly increased fighter capability and required minimal technology for employment in conventional conflicts,” Young wrote. 

Earning stripes

While the AIM-9’s 60% kill rate in testing and early operations such as the 1958 Taiwan Strait Crisis showed great promise, the Vietnam War exposed the missile’s shortcomings. North Vietnamese fighter pilots figured out how to outmaneuver the missile, Young wrote, and American aircrews were undertrained on both the Sidewinder’s capabilities and on dogfighting enemy aircraft like MiG-17s. The 60% kill rate promised before the war fell to about 10 to 15% by the end of 1968.

Subscribe to Task & Purpose Today. Get the latest military news, entertainment, and gear in your inbox daily.

The Air Force and Navy both worked to improve the missile’s performance through various technical upgrades, but the Navy showed the greatest gains in performance by improving the training of its aircrew through efforts like the U.S. Navy Fighter Weapons School (better known as Top Gun). By the end of 1972, “the Navy’s Phantom II-Sidewinder combination became so deadly that NVAF MiGs began circumventing combat,” Young wrote.

So began a long win streak for the Sidewinder, which continued to improve through technical upgrades such as the release of the AIM-9L and AIM-9M. Sidewinders fired from U.S. Navy F-14s destroyed two Libyan Su-22s in 1981, helped the Israeli Air Force dominate Syrian MiG-21s and MiG-23s over Lebanon in 1982, and arguably saved the United Kingdom’s air war against Argentinian Mirage IIIs and other aircraft during the 1982 Falklands War. The Sidewinder continued to prove its worth during the Gulf War, where it shot down Iraqi MiG-21s, MiG-23s, and even a Mi-8 helicopter

aim-9 sidewinder
A U.S. Air Force weapons load crew team from the 44th Aircraft Maintenance Unit carry an AIM-9L/M Sidewinder missile to an F-15 Eagle fighter aircraft during a quarterly weapons load competition April 3, 2017, at Kadena Air Base, Japan (Naoto Anazawa/U.S. Air Force)

But why is the U.S. military still using the missile now, almost 70 years after its first successful test? Part of the answer is that it still works, especially after all the technical upgrades that make the current AIM-9X a much more capable beast than its ancestors. Indeed, when Boeing won a contract in 2010 to support Sidewinder operations through to 2055, Air Force spokesperson Stephanie Powell said in a press release that the missile’s relatively low cost, versatility, and reliability made it “very possible that the Sidewinder will remain in Air Force inventories through the late 21st century.”

Balloon popper

McLean and his team of China Lake engineers may not have suspected back in the 1950s that the weapon they designed to take down nimble enemy aircraft would be used to destroy relatively static balloons or UFOs at the edge of space. In fact, when an Air Force F-22 pilot used an AIM-9X to destroy a Chinese spy balloon at about 60,000 feet above the Earth last week, it may have been the first time a Sidewinder ever reached such distant heights.

“I don’t know that they’ve tested an AIM-9 at that altitude,” the commander of the North American Aerospace Defense Command, Gen. Glen VanHerck, told reporters on Feb. 6. 

Another option to destroy the balloon was the AIM-120, a radar-guided missile, but the decision to use the AIM-9 instead “goes back to safety considerations and effectiveness,” VanHerck said. “You know, the AIM-120 has a significantly-larger range, a significantly-larger missile warhead.”

aim-9x sidewinder
An F-15E Strike Eagle weapons load crew team lifts an AIM-9X Sidewinder missile to attach to a pylon July 15, 2019, at Al Dhafra Air Base, United Arab Emirates. The AIM-9X is an advanced infrared missile and the newest of the Sidewinder family of short-range air-to-air missiles carried on a wide range of fighter jets. (Staff Sgt. Chris Thornbury/U.S. Air Force)

The AIM-9X was considered to be a more safe but equally effective option compared to the AIM-120, VanHerck explained. Still, the AIM-9X can cost about a third to half a million dollars a pop, according to Department of Defense budget documents

Are there less expensive options for bringing down these balloons and UFOs, such as the cannons aboard Air Force fighter jets? Probably not without considerable safety risks. For example, the balloon was so high up that even the F-22, with its maximum ceiling of around 65,000 feet, was reaching the edge of its capabilities, as our colleagues at The War Zone reported

That high up, closing to gun range with the balloon would have added unnecessary risk to the mission. The shells fired from such a gun run would likely cause only small holes in the balloon before flying for miles below, where “their kinetic energy alone” would be dangerous to anybody on the ground, The War Zone wrote.

If the current pace keeps up, the AIM-9X will have quite a few more kills to its name, though it is still unclear what exact kinds of aircraft were killed. Either way, the Sidewinder has proved once again that it is not going by the wayside anytime soon.

The latest on Task & Purpose

Want to write for Task & Purpose? Click here