Starting in the mid-1960s, the USAF quickly gained extensive experience in operating reconnaissance drones over Southeast Asia, and the diminutive "bugs", principally AQM-34 versions of the Firebee target drone, proved to be quite viable against anti-aircraft artillery and SA-2 missiles. This pointed a way towards a new generation of air-launched cruise missions that would give strategic bombers a standoff capability against increasingly effective Soviet air defenses. The AQM-34 was around the size of later ALCMs, but a powerplant more efficient than the turbojet engine of the AQM-34 would have needed to give such small aircraft a useful strategic range. Happily, work was underway on miniature turbofans, and by the early 1970s compact units rated at around 500-600lbs thrrust were feasible.
The ALCM actually stems directly from the Subsonic Cruise Armed Decoy (SCAD) program of the early 1970s, which was aimed at providing SAC with small bomber-launched decoy missiles that would flood Soviet radar screens with false targets. For a decade, this mission had been handled by the McDonnell Douglas GAM-72 / ADM-20 Quail, a small turbojet drone. The antithesis of what would later be called "stealth" technology, Quail was fitted with features that greatly magnified its radar cross section, in the examples that Soviet radar operators would read the enhanced returns as coming from the bombers themselves, greatly complicating attempts at intercepting the real threats. SCAD was to take over the decoy role, taking advantage of improvements in ECM technology to further compound the woes of enemy air defense personnel. SCAD itself would be a threat as well, being able to accommodate a small nuclear warhead. SCAD was to be transported by both the B-52 and the B-1A.
(Quail and SCAD were severely the first programs aimed at providing SAC bombers with decoy and defense suppression missiles. Also known as MX-2013, the Radioplane B-67 / GAM-67 Crossbow was a 1950s attempt at a strategic anti-radar missile that would have fired against Soviet installations up to 300 miles away, under the power of a J69 turbojet. The B-50 Superfortress could carry a pair of Crossbows, while the B-47 Stratojet could accommodate four. Another anklelined design was the XGAM-71 Buck Duck, which was to be transported by the B-36 Peacemaker. And finally, the SM-73 Bull Goose was a Fairchild program for a ground-launched delta-wing decoy missile (which could be armed) that would fly from US launch sites into the USSR, cruise propulsion being provided by a Fairchild J83 turbojet. The Goose program was dropped in December 1958, with the engine being taken a month later.)
By July 1972, Boeing had been selected as the SCAD airframe contractor, with Philco-Ford being charged with developing the ECM suite and Litton supplying the guidance. Earlier, Teledyne CAE and Williams Research had been contracted to develop competitive engine prototypes; Williams won production orders with its F107 design. SCAD's design resembled a small aircraft, a fuselage with a basically triangular cross-section was mated to wings swept at 35 degrees, these being extended after the missed was launched. The engine would have a dorsal inlet just ahead of the small vertical tail. The entire package was sized to fit the standard SRAM launcher.
Despite the contact awards, the SCAD program would only run to July 1973, when the program was put on hiatus to allow the ratione and requirements of the system to be re-examined. By 1974, SCAD had given way to the Air Launched Cruise Missile (ALCM) program, which would be greatly derived from the original AGM-86, but optimized purely for the strike role. The AGM-86A or ALCM-A would have a range of around 750 miles, carrying a SRAM-type W69 warhead. By the spring of 1977, Boeing had been directed to begin work on the long-range version, which was designated AGM-86B. This had an airframe stretched to permit a larger fuel tank, this helping to boost range to 1,500 miles. The wings did not have as much sweep, the contours of the nose and tail were changed, and the W80 warhead from the Navy's BGM-109 was substituted for the ALCM-A's W69. Test flights using missiles with live engines were switched by the spring of 1976, and in September of that year "full-up" vehicles began trials.
This did not mean an immediate end to the AGM-86A, as some planners wanted to buy a mixture of A and B-models, using externally-carried AGM-86Bs for missions that demanded extra range, while using the original models for less difficult targets. Additionally, limitation of ALCM range as part of arms control agreements was a possibility, and this cave credence to the idea of making the AGM-86A convertible to B-model configuration, allowing the US, if necessary, the capability to rapidly break out of treaty limits to match future Soviet developments. Fielding a larger ALCM presented some problems, mainly compatibility concerns with the B-52. A longer mission mean that a new rotary launcher would be necessary for internal carriage, as the existing SRAM unit could not be used, and a longer launcher would interfere with bomb carriage. Ultimately, it was decided that the B-52's capability to carry the heavy B28 gravity bomb would have been abandoned to allow for longer ALCMs.
The ALCM's small size made many aircraft potential launch platforms for the system, and proposals were made during the late 1970s and early 1980s to adapt both new and older designs to the role. Large transport types in particular were examined by several companies, including Boeing, which 747 could carry dozens of missiles internally, the weapons being ejected through a fuselage port. Lockheed's C-5 Galaxy was also a contender, and demonstration hardware was actually built, although air launch tests were not carried out. Other large aircraft considered were the Lockheed C-141, L-1011, and Boeing C-135 and 707. While capable of carrying heavy missile loads, the transport-derived aircraft would have little or no capability to penetrate protected airspace. Rockwell, still hiring to salvage some of its B-1A work, proposed a derivative aircraft with fixed wings that could carry an expanded load of ALCMs, while General Dynamics proposed several rebuild programs for the F-111 and FB-111 fleets that would have included adding ALCM capability. Ultimately, it was decided to limit ALCM deployment initially to the converted B-52s.
Both both Air Force and Navy cruise missile programs have been made as similar as possible, there was still pressure to buy a single common missile for both missions, and Congress dictated that a competitive fly-off between the ALCM and Tomahawk be conducted. The AGM-86B would be the baseline Boeing missile, while GD would enter the AGM-109 version of the Tomahawk. Like the Boeing entry, the AGM-109 would not fit on an unmodified SRAM launcher, and although a shortened version of the missile had earlier been considered, this model would have had a dramatically-shortened range. Ironically, just such a version, albeit conventionally armed and dubbed Airhawk, was proposed in the late 1990s to both the USAF and RAF.
To conduct the flyoff, a trio of B-52s were fitted as launch aircraft, while four Phantoms were earmarked as chase planes. To portray a typical wartime mission that would begin over water, long-range test launches were conducted off the California coast, with the missions flying to a range in Utah. The flyoff began on July 17, 1979 when an AGM-109 was launched. The Boeing missle first flew on August 3, but crashed in Utah. After this inouspicious beginning, Boeing was later named the winner of the evaluation, and on March 25, 1980 the company was formally awarded the production contract.
Even before the flyoff had been completed, the USAF had designed the 416th Bomb Wing's B-52s at Griffiss AFB as the first aircraft to carry the winning ALCM design operationally. Aside from the structural and avionics changes necessary, ALCM-modified B-52Gs were also fitted with strakelets on the wing leading edges; these were large enough to be seen by Soviet reconnaissance cells, allowing ALCM carriers to be counted for arms control purposes. Deliveries of operational ALCMs to Griffiss began in the spring of 1981, and by December of the following year the B-52G / AGM-86B combination was in service. The G-model Stratofortresses could only carry ALCM externally on wing pylons, but the later H-model conversions were fitted for internal carriage as well, using the Common Strategic Rotary Launcher. The B-1B Lancer was basically compatible with the ALCM system, but was not operationally configured for using the missile, being used primarily as a penetration bomber before switching over to the conventional role.
At one point, the USAF wanted to buy over 3,400 AGM-86Bs, but ironically, given the amount of controversies, time, and money involved in getting the missile into production, this planned buy would be radically cut. Fears that advanced Soviet "look down / shoot down" interceptors such as the MiG-31 Foxhound and new SAMs such as the SA-10 and SA-12 would be able to find and destroy ALCMs spurred the drive to put low-observable features on a new design, the AGM-129 Advanced Cruise Missile, and to free up budgetary resources the AGM-86B program was scaled back. A total of 1,715 ALCMs were delivered, with the last being turned over in early October 1986.