AIM-9L: The Super-Sidewinder
The birth of the third-generation Sidewinder was shaped by air-to-air missile problems in the Vietnam War, in which the navy and air force had used different versions and learned different lessons. The navy used good Sidewinders—the D, G, and H versions—and saw that many of the failures occurred because pilots had fired them without proper training or understanding. In conjunction with a general overhaul of air combat maneuver training—generated by the Ault Report (see chap. 16)—increased emphasis was placed on Sidewinder use at the new Top Gun Fighter Weapons School at NAS Miramar. This seemed to solve the navy’s problems.
The air force, meanwhile, had been firing the E and J versions, which were not adequate. When the air force analyzed failures with its Sidewinders, the problem appeared to be reliability. The air force solution was to build smaller and cheaper missiles, and fire more of them, so the service approached Hughes, Ford, and General Dynamics to help. The air force was well into this program (known as CLAW) when William Perry, the Defense Department’s deputy director of research and engineering (later secretary of defense) took charge. Perry told the air force to go instead to China Lake. The Pentagon had decided it was time for the two services to get together on the development of a common missile.
China Lake welcomed the air force and treated the officers to a discussion of new technologies: wide-angle seekers, helmet-mounted sights, and thrust-vector control (steering jets instead of canards). Thrust-vector control promised missiles that could turn on a dime. Helmet-mounted sights—already tested in helicopters for miniguns—would allow faster pilot response. China Lake was putting together an advanced missile called Agile that would have all these features, as well as an advanced Sidewinder designated AIM-9K that would use only the wider gimbal-angle seeker.
China Lake argued that the new technologies would create a genuine dogfight missile. While the air force was familiar with these technologies—and was working on the AIM-82 missile that incorporated some of them—in the end it decided that the exotic technologies were too big a risk and opted for an upgrade rather than a new missile. Again, China Lake had just the program: the AIM-9H Product Improvement Package (PIP).
In 1970 Walt Freitag had been monitoring AIM-9H as it went into pilot production, assuming that it would be “the last Sidewinder.” But Roland Baker, manager of the Chaparral program, decided that Chaparral could be improved and asked Freitag to carry out an “Advanced Chaparral Study.” Freitag asked a young engineer named Dick Schmitt to help him and the two—recognizing that Sidewinder still had a lot of life—widened the focus to the entire Sidewinder program. The “Advanced Chaparral Study” soon became a “30-day study” to define what might be done with Sidewinder. The strawman missile that emerged was the AIM-9H PIP.
Raytheon, which had been making Sidewinders for nearly a decade, immediately went on alert. Ed Paul, Raytheon’s Sidewinder program manager, had started a multiyear study of detectors in 1968 because he felt Raytheon had to keep working in phase with China Lake. When China Lake did its 30-day study, Raytheon ran its own 30-day study. When China Lake did a 60-day study following the 30-day study, so did Raytheon.
China Lake decided the key to success was a better detector. Previous Sidewinders had used detectors that were best at detecting short- and medium-wavelength infrared radiation—the kind given off by jet engines and their exhaust plumes. But an indium antimonide detector would detect the longer wavelengths associated with warm aircraft parts, such as nose cones, giving the missile “all-aspect capability” (ALASCA), including the long-desired head-on shot. Radar missiles had this all-aspect capability, of course, but at the cost of higher complexity. Sidewinder kept it simple.
Using indium antimonide for the detector was not a new idea. In fact, Benton’s Optical Design Branch had wanted to put one into the AIM-9H, but the navy had shown scant interest in major changes to the Sidewinder, and in most respects the 9H was simply a solid-state version of the 9D. The next missile would be a chance to see what indium antimonide might do. Ed Paul immediately told his people at Raytheon to begin studying indium antimonide detectors.
Meanwhile, Ford Aerospace had approached Luke Biberman, then at the Institute for Defense Analysis, regarding Chaparral improvements. The navy then also approached Biberman regarding Sidewinder improvements. Raytheon decided it would support the navy’s effort.
This led to a scramble between Ford and Raytheon over who would get the next Sidewinder development contract. Complicating matters, the navy wanted amplitude-modulated (AM) scanners while the air force wanted to use frequency-modulation (FM). Raytheon’s Dick Beckerleg came up with a synthesis, an AM-FM system; this kind of problem-solving convinced Biberman that Raytheon was better prepared than Ford, and Raytheon got the job.
When it was clear that the air force was interested in the new detector, Benton’s team got to work immediately on a feasibility study. Benton got Freitag’s electronics group to make an absolute minimum of needed changes in signal processing and an indium antimonide detector was soon mounted on the missile. The modified AIM-9D was then taken out and fired from a Chaparral (ground) mount, the fastest way to get a test.
For no apparent reason, the missile missed the drone by ten to fifteen feet. Nonetheless, this was enough to show the idea would work, and it gained the team approval for a development program. China Lake, Raytheon, and Biberman worked out final specifications, which were issued by Secretary of Defense David Packard in June 1971.
Raytheon, meanwhile, had developed the HX prototype—a Sidewinder with “rate bias.” Like lead bias, rate bias aimed the missile forward of the hot tail or the plume in the afterburner. It was such a good idea that the navy forced China Lake to accept it. Getting it to work, however, proved difficult. In March 1972 Freitag’s team carried out its first flight test at China Lake. The missile literally hit the drone on the nose. The team was elated, but the result was not what they expected: Why did it hit the nose?
Yet the missile had worked. When many of the following shots passed in front of the drone instead of hitting it, however, the team knew it had a problem. Fortunately, the fifteen engineers were an active team under Freitag’s gifted leadership. “It was a skunk works, a small number of people really making technical decisions,” Schmitt said. Fortunately, also, General Dynamics had discovered and solved a similar problem with rate bias on its Stinger antiaircraft missile. Adding an automatic gain control to the rate bias circuit solved the problem.
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The air force was ambivalent during the design phase, and when troubles came, it was eager to dump the project. In 1973, when the 9L was in trouble, the air force wanted a shoot-off to show that its AIM-9J was not such a bad weapon after all. Raytheon brought a version of the AIM-9H to the tests, fitted with an internal gas bottle, so it would fit on air force launchers. The Raytheon “H Squared” proved far superior to the 9J, and the air force backed off.
What would become the Sidewinder AIM-9L soon got back on track, but the air force, still skeptical of its ability to hit a plane in afterburner, scheduled fifty tests with QF-4 Phantom drones to verify the capability. The 9Ls took out one expensive drone after another. The air force showed up at China Lake, asking for a slight miss bias in the missile, so its drones would be spared. It got little sympathy.
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All the efforts paid off, and the air force finally relented; air force captain Mike Hall, a Sidewinder test pilot, played a key role.
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An “Interim Agile”
By January 1975 the AIM-9L was ready for joint navy–air force evaluation. That month five missiles were fired against QF-102 drones—planes that, ironically, had been designed to fire Falcons. A total of forty-six firings took place, the last on 1 March 1975. In 1976 Raytheon and Ford Aerospace put the missile into production, ending years of separate navy and air force procurement. The joint service missile was most critical for the air force, which finally got a missile with the range of the AIM-9D and the new all-aspect capability.
The AIM-9L was an “extraordinarily lethal weapon.” Tom Amlie called it “a death ray.” The 9L’s double-delta canards gave it an incredible 35-G capability, almost five times what average pilots can with-stand, making it virtually impossible to out-turn the missile. Air force colonel Walter Vrablic told Raytheon’s Russ Whynot that “when China Lake invented the 9L, I knew it was time to get out of the fighter pilot business.”
