AGM-86B ALCM Air-launched cruise missile

[Zarvan]

The AGM-86 ALCM was the first US stand-off nuclear weapon, that could be launched from an aircraft



Country of origin United States
Entered service 1982
Missile
Missile length 6.32 m
Missile diameter 0.62 m
Wing span 3.66 m
Missile weight 1 450 kg
Warhead weight 130 kg
Warhead type Nuclear (5 - 150 kT)
Range of fire 2 400+ km
Speed 800 km/h
CEP 300 m
Guidance Terrain-following radar and INS
Launch platforms B-52G/H


The Boeing AGM-86B ALCM (Air-Launched Cruise Missile) is the primary nuclear munition of the US Air Force (USAF). As of early 2016 it is the only air-launched missile in the US inventory with a nuclear warhead. As a result, it plays a pivotal role in the US government's strategic deterrence policies.

Though this weapon itself is well-known, its origins --- which by all accounts were quite strange --- are today quite obscure. It was not originally supposed to be a cruise missile at all; when it was, it was also supposed to perform two different missions simultaneously; by the time the ALCM began to take shape as a single-mission weapon, it suddenly became the program most fiercely-opposed by the armed service that it was meant for; it was canceled as a result, but it was revived in later years, and (much to the chagrin of the USAF at the time) it eventually entered service; and since then, the USAF has extolled it, as though they never had an issue with it.

Development began in January of 1968 as the SCAD ("Subsonic Cruise Aircraft Decoy"), an airborne decoy meant to mimic the radar signature of a bomber carrying nuclear ordnance, which was to replace the troublesome ADM-20 Quail in that role. SCAD was formally approved in June of 1970, and work began on a prototype, the ZAGM-86A. At some point in the early 1970s however, it occurred to the USAF that the SCAD could itself be used to deliver a nuclear warhead, and could do so relatively accurately after flying a great distance from the launch point. The program was at this point split into two parallel projects; SCUD ("Subsonic Cruise Unarmed Decoy"), and SCAD, which was now backronymed to mean "Subsonic Cruise Armed Decoy". The idea was that in the event of a nuclear offensive (most likely against the USSR), US bombers employing the SCAD and SCUD now had an additional layer of ambiguity to operate under inside enemy airspace, as any radar contact could be a SCAD, a SCUD, or a bomber armed with nuclear warheads (possibly being additional SCADs).

However, when the USAF began pressing hard for the introduction of a new bomber during the early 1970s, their attitude toward SCAD and SCUD took an abrupt turn. The B-1A Excalibur strategic bomber was to use raw speed and free-fall ordnance to attack enemy territory, and because it was one of the most expensive items in the USAF budget, air-launched cruise missiles were seen as unwanted competition. Critics of the B-1 had already begun agitating for the use of cruise missiles instead of B-1s, as older B-52s could be made to launch them. This was not well-received by the USAF's leadership (nor Rockwell, the B-1A's manufacturer, who were faced with possible bankruptcy if they didn't sell the B-1). There was even discussion outside the USAF of replacing bombers with cruise missiles entirely, no doubt reminding some of such prior debacles as the Snark intercontinental cruise missile (whose guidance system was so bad that at least one example, aimed at the Faroe Islands in the North Atlantic, instead landed in Brazil), and attempts by the Eisenhower and Kennedy administrations to totally replace bombers with ICBMs.

Citing cost and schedule overruns, and a seemingly uncountable increase in complexity for the ZAGM-86 and the program developing it (which somehow hadn't been an issue when these problems emerged years prior), the USAF canceled the program in June of 1973. Behind the scenes, what the USAF's leaders actually feared was that introducing the ZAGM-86 into service would eliminate the case for the B-1A. The cancellation was short-lived, however, because the USAF realized that because the Navy was developing its own cruise missile (the SLCM, or Sea-Launched Cruise Missile, a program that resulted in the BGM-109 Tomahawk), they might lose the entire mission to the Navy --- high-speed bomber or not. In response (at least in part) to the SLCM program, SCAD was renamed ALCM (Air Launched Cruise Missile), and the SCUD portion of the program was eventually discontinued.

Thus, in September of 1974, Boeing was awarded a contract to complete development of the ZAGM-86. Only now, there was a catch; as a thinly-veiled safeguard against cancellation of the B-1A, the ZAGM-86 had to be shortened, for the purpose of fitting into the bomb bay of that aircraft. The USAF "sanitized" the back-story on requirement, stating that they wanted the ZAGM-86 to fit onto the existing pylons for the AGM-69 SRAM tactical nuclear missile already in service (what they didn't let-on was that the only aircraft in the USAF inventory then outfitted to carry the SRAM were the FB-111 and B-52, but they carried this weapon externally).

Congress in 1977 had also taken an interest in a single cruise missile model for use by both the US Navy and USAF (the JCMP, or "Joint Cruise Missile Project"). Neither the US Navy nor USAF cared much for the prospects of operating one another's missiles, and the ZAGM-109 had proven more unwieldy for a bomber to carry than the ZAGM-86, while the former was less suitable for launch from submarines than the latter. The outcome of the JCMP program was nonetheless productive, as both services agreed to use common components in their respective cruise missiles, including the engine and guidance system.

Another watershed event occurred in the same timeframe as JCMP was the termination of the B-1 program by President Jimmy Carter. This triggered a crisis in the USAF, because instead of a debate over whether the USAF should operate B-52s with cruise missiles or the B-1, now they no longer had a choice. Many officials hoped the next presidential administration would revive the B-1 program (which did in fact occur), but the B-1 wouldn't enter service until well into the future if it could even be revived at all; left with no other choice, the USAF fully-embraced the ALCM.

As there was no longer a need to squeeze the ALCM into the bomb bay of a B-1, the USAF had Boeing discontinue the AGM-86A in favor of the original, larger version. Initially designated the ERV ALCM, the larger missile was still compact enough for several to be carried inside the B-52's internal bay, and was the model that competed with the ZAGM-109 during the JCMP competition. Development continued for several more years, and the larger ERV ALCM entered service with the USAF in August of 1981 as the AGM-86B ALCM.

Interestingly, although the B-1 bomber finally entered service with the USAF later in the same decade, and it too was expanded into a "B" model, the original internal bay dimensions were retained, making the B-1B Lancer too cramped to carry the AGM-86B. The USAF also declined to make the B-2 Spirit bomber compatible with this missile, deciding that the AGM-86B was too easily detected for use in the B-2's mission; this led to the development of what would become the AGM-129 ACM. As a result, the only aircraft presently configured to employ the ALCM is the B-52.

The AGM-86B has a long fuselage with a trapezoidal cross-section, a tapered, slightly rounded nosecone, and rounded corners. The sides of the ALCM are flat and sloped inward, while the topside is rounded, and the belly is shallowly peaked. The fin-like cantilever wings are short and extremely narrow, and are recessed into the belly of the missile until it is launched. Two small, trapezoidal horizontal stabilizers are mounted on the tail of the missile, which are folded-up against the fuselage until launch. When unfolded, they lock into an anhedral position. The tailfin is also small and trapezoidal, and is wrapped around the left side of the fuselage prior to launch. A tubular airscoop, which blends neatly into the aft fuselage in its aft section, is mounted in front of the tailfin. The thrust nozzle for the ALCM is very small, and mounted at the base of the tail. Finally, it is worth noting that the AGM-86C/D CALCM have an almost identical appearance, making these conventionally-armed missiles difficult to distinguish from the nuclear AGB-86B ALCM.

The B-52G (now retired) and B-52H can carry the ALCM on its external hardpoints, or inside its bomb bay. When mounted externally, a total of 12 ALCMs are mounted on each pylon, in two tandem triple clusters. The ALCM is carried in the bomb bat on a rotating launch rack, which hold up to 8 missiles; though the B-52 could probably carry more missiles if they were stacked-up in the internal bay (in the same fashion as it carries bombs), the rotating rack eliminates the dilemma of having one or more missiles trapped above another that fails to release (a malfunction known as a "hung munition", which is not an uncommon problem). The trapezoidal cross-section of the ALCM also contributes heavily to its ability to be carried in such large numbers on both the pylons and the rotating rack, as it allows more to be crammed into a given volume than a purely cylindrical missile --- this can clearly be seen in photographs of rotating racks fully-laden with ALCMs.

The guidance system used in the AGM-86B consists of a McDonnell-Douglas AN/DPW-23 Terrain Following Radar (TFR), with a Terrain Contour Matching (TERCOM ) capability. TERCOM allows the missile to fly on a preprogrammed route, via image recognition of a series of radar photographs of the terrain. The addition of Instrument Navigation System (INS) guidance helps steer the missile onto this course upon launch, and maintain the proper heading, both via compass. This makes the missile fully autonomous upon release and impossible for enemy action to divert, allowing the bomber that launched it to immediately begin another missile run, or beat a hasty retreat.

However, TERCOM is also quite delicate, and is easily defeated by jamming or interference, and terrain covered by snow, ice, or inundated with water has been found to yield false radar returns. Experience with the BGM-109 Tomahawk (which uses the same guidance method) also demonstrates that missiles with TERCOM guidance can easily drift off course, especially if much of the terrain they have to fly over is largely featureless (such as in the Arabian Desert); sometimes, when the TFR finally began to receive returns from unfamiliar landmarks, effectively causing the missile to fly aimlessly until it had flown the required distance, and then plunged into the ground. Notably, errant Tomahawks launched in the 2003 Invasion of Iraq landed in locations as far off target as Turkey, Iran, and Syria. It goes without saying, but such imprecision has frightening implications for a nuclear-tipped cruise missile with a range of over 2 000 km.

The AGM-86B is powered by a Williams F107-WR-100 turbofan engine, generating 2.7 kN of thrust; some examples are powered by the largely similar F107-WR-101 engine, with the same power output. The missile briefly produces a line of thin, black smoke after launch, suggesting that it uses a black powder-based starter cartridge (though other factors could cause the smoke trail to be darker during the first seconds of propulsion). As the missile is already moving through the air at considerable speed when released from an aircraft, a rocket booster is not employed in the AGM-86B, unlike the US Navy's counterpart, the BGM-109 Tomahawk (which otherwise employs the same F107 engine).

The AGM-86B only delivers one type of munition, the W80 thermonuclear warhead. This is a variable yield warhead, with which the aircrew can selectively "dial-in" the force of the blast. The lowest setting is 5 kT, while the highest is 150 kT. The W80 was produced in two variants, the W80-1 and subsequent W80-0; the differences between the attributes of these models is unclear.

Approximately 1 715 AGM-86Bs have been manufactured, from 1980 to 1986. Of these, 528 remain in the US inventory, with another 500 being retired from 2007 onward. Several-hundred of the others were converted into CALCMs in earlier years. The unit cost of an AGM-86B is approximately US$1 million, though assembly lines used to manufacture the AGM-86B no longer have the ability to do so. Due to the geopolitically sensitive nature of nuclear arms, the AGM-86B is not available for export.

The AGM-86B has made several notable appearances in media, notably in the movie Never Say Never Again, where it was incorrectly depicted as being launched from a B-1A (only the AGM-86A was compatible with the B-1 series; moreover, in the scenes showing the missiles being prepared under the aircraft prior to flight, the aircraft's belly is clearly that of a Concorde airliner); the film also incorrectly depicts the AGM-86B as being powered by an afterburning engine (there are no afterburning F107s).

The future of the AGM-86B ALCM remains uncertain, as a suitable successor has yet to materialize, despite the USAF'sLong Range Stand-Off requirement for such a weapon. Its role is possibly more important than ever before, due to the retirement of the subsequent AGM-129 ACM in 2012, and the slowly dwindling number of operational B-52Hs to launch them. The remaining missiles have been given a SLEP (Service Life Extension Program) to extend their service into as far into the future as 2030, but the 1970s-era technology of the ALCM has arguably been obsolete in the nuclear attack role for decades.

It is also possible that the remaining AGM-86Bs will be converted into conventionally-armed CALCM missiles (which had been done before); though given that no such conversion has been made for years, this outcome is increasingly becoming improbable.



Variants



SCAD: "Subsonic Cruise Armed Decoy"; the original concept for the ALCM. Evolved into the AGM-86A.

SCUD: "Subsonic Cruise Unarmed Decoy"; airborne decoy version of the SCAD. Did not enter service.

AGM-86A ALCM: Original design with a reduced length for the B-1A's bomb bay. Did not enter service.

AGM-86B ALCM: Enlarged version of the AGM-86A, with a radically enlarged and re-shaped fuselage.

AGM-86C/D CALCM: Conventionally-armed version of the ALCM. Described on a separate page.

http://www.military-today.com/missiles/agm_86b_alcm.htm

 

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