AGM-86 ALCM

The ALCM traces its history to the ADM-20 Quail missile, which began development in February 1956. Quail was the ultimate outcome of several similar programs to develop a small decoy aircraft that would be launched from bombers during their approach to targets, presenting false targets to saturate the defenses and allow the bombers to escape an attack. The small jet-powered drone aircraft had a simple inertial navigation system (INS) that allowed it to fly a pre-programmed course that would make it visible to known Soviet defensive sites. A number of radar jammers and radar reflectors were intended to make it appear like a B-52 on a radar display.

Quail was designed in the mid-1950s when the normal attack profile for a strategic bomber was to fly as high and fast as possible to reduce the time the defenders had to respond to the aircraft before it flew out of range. This was effective against interceptor aircraft but of little use against surface-to-air missiles (SAMs), whose attack times were measured in seconds.

This led to the adoption of low-level attacks, where the bombers would fly below the radar horizon so they could not be seen on ground-based radars. Quail, originally designed for the high-altitude mission, was modified with the addition of a barometric altimeter to allow it to fly at lower altitudes. Doing so seriously limited its effective range and flight time. In the early 1960s, the Air Force began to question the usefulness of Quail in the face of improving Soviet defenses.

Looking for another solution to the Soviet SAM problem, in 1964 the Air Force began developing a new system that would directly attack the missile sites rather than confuse them. This emerged as the AGM-69 SRAM, with a range of about 50 nautical miles (93 km; 58 mi), allowing it to be launched from outside the roughly 20 nautical miles (37 km; 23 mi) range of the SA-2 Guideline missiles it faced. Flying at Mach 3, it quickly flew out in front of the bombers, reaching the missile site before the bomber flew into the range of the SA-2.

While highly capable against known missile locations, SRAM could do nothing to defend against unknown sites, nor help with the problem of interceptor aircraft. To deal with these threats, Quail continued to be carried, typically in pairs, providing some defense against these other threats. However, by the late 1960s the Air Force concluded "that the Quail was only slightly better than nothing."

In January 1968, a new requirement emerged for a modern version of Quail for this new mission, the Subsonic Cruise Aircraft Decoy, or SCAD. SCAD was designed specifically to fit onto the same rotary launcher used by SRAM, allowing a single aircraft to carry multiple SRAM and SCAD and launch either at any time. This led to it being the same 14 foot (4.3 m) length as SRAM, and the use of a fuselage with a triangular cross-section, which maximized the usable volume on the rotary launchers. The system was otherwise similar to Quail, using a simple inertial navigation system (INS) allowing the missile to fly a pre-programmed course.

Soon after development began, it was noted that the very small nuclear warheads being developed at that time could be fit to SCAD without seriously affecting its performance as a decoy. This would allow it to act as a decoy for much of its flight, and then deliberately approach a selected defensive site and attack it. As such, the program was renamed Subsonic Cruise Armed Decoy, retaining the SCAD acronym.

For this role, the accuracy of the original INS guidance hardware was not enough. While a similar system was also used in SRAM, its shorter range and much shorter flight times meant the drift rate of the system was not a serious concern as long as the bomber could feed it accurate information just before launch, to "zero out" the drift. In contrast, SCAD was designed to fly over much longer ranges and slower speeds, resulting in longer flight times and increasing the problem with drift; even with the drift "zeroed out" just before launch, subsequent drift during the longer flight would accumulate to an unacceptable error. To provide the accuracy needed to attack the SAM sites with a small warhead, some system was needed to zero out the drift in-flight, and for this need, a radar-based TERCOM system was added.

Development was approved in July 1970, and it was given the designation ZAGM-86A, the Z indicating its initial development status.

The original ALCM was much smaller than later models, and had a pointed nose profile.

As SCAD moved from the pure-decoy role to decoy-and-attack, this meant it would be able to carry out the same mission as SRAM, but from much longer range. This would reduce the need for a decoy. Accordingly, in June 1973, SCAD was canceled in favor of a system dedicated purely to the long-range attack mission. The original designation number remained, but the name changed to reflect the new mission, becoming the Air Launched Cruise Missile, or ALCM.

The first example, similar to the original SCAD in most ways, flew for the first time in March 1976, and its new guidance system was first tested that September. In January 1977, the missile was ordered into full-scale production. Compared to the models that entered service in the 1980s, the A-model had a distinctive look; the nose tapered sharply to a triangular point giving it a shark-like appearance, compared to the later models which had a more rounded conventional appearance.

The fuselage stretch for the ERV is evident in Udvar-Hazy Center's AGM-86B.

Meanwhile, the Air Force had also issued a requirement for a version with a much longer 1,500 nautical miles (2,800 km; 1,700 mi) range. This would allow the bombers to launch their missiles from far off the Russian coast, placing it outside the range of the interceptors as well. To reach the intended range, this new Extended Range Version (ERV) would have to be lengthened to contain more fuel, or external fuel tanks would have to be added. Either change would make it too large to fit on the SRAM launchers and the extended-fuselage version would be too large to fit in the bomb bay of the new B-1 Lancer bomber. The Air Force intended to replace the original ALCM with the new version at some future date.

The Navy was also in the midst of its own cruise missile project, the Sea-Launched Cruise Missile (SLCM), which ultimately emerged as the BGM-109 Tomahawk, which was similar to ALCM in many ways. In 1977, the Air Force and Navy were ordered to collaborate under the "Joint Cruise Missile Project", JCMP, with the intention of using as many parts in common as possible. After considering the two designs, the Air Force agreed to modify the ALCM with the SLCM's McDonnell Douglas AN/DPW-23 TERCOM system, as well as using its Williams F107 turbofan engine.

While the JCMP program was taking place, the B-1 was canceled. This eliminated the need for ALCM to fit in the B-1's bomb bay, and the length limitations that implied. The Air Force decided to cancel production of the A-model ALCM, and replace it with either an air-launched version of the SLCM, or the ERV. The ERV flew in August 1979, and was declared the winner of the head-to-head fly-off against the SLCM in March 1980.

Production of the initial 225 AGM-86B missiles began in fiscal year 1980. It entered operational use on the B-52H in August 1981 and became its primary weapon in December 1982. Production of a total 1,715 missiles was completed in October 1986. The air-launched cruise missile had become operational four years earlier, in December 1982. More than 100 launches have taken place since then, with a 90% approximate success rate.

In June 1986 a limited number of AGM-86B missiles were converted to carry a high-explosive blast/fragmentation warhead and an internal GPS. They were redesignated as the AGM-86C CALCM. This modification also replaced the B model's TERCOM and integrated a GPS capability with the existing inertial navigation system computer .[2]

In 1996 and 1997, 200 additional CALCMs were produced from excess ALCMs. These missiles, designated Block I, incorporate improvements such as a larger and improved conventional payload (1,360 kg, 3,000 lb blast class), a multi-channel GPS receiver and integration of the buffer box into the GPS receiver. The upgraded avionics package was retrofitted into all existing CALCM (Block 0) so all AGM-86C missiles are electronically identical.[2]

The nuclear armed AGM-86B uses a terrain contour-matching guidance system (TERCOM) to fly to its assigned target.[2]

The AGM-86C/D CALCM carries a conventional high-explosive payload rather than a thermonuclear payload. This is a fragmentation warhead in the AGM-86C and a unitary penetrating warhead in the AGM-86D. The AGM-86C/D uses an onboard Global Positioning System (GPS) coupled with its inertial navigation system (INS) to navigate in flight. This allows the missile to guide itself to the target with pinpoint accuracy. Litton Guidance and Control, and Interstate Electronics Corp. were the guidance contractors for the C model.[2]