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AGM-129 ACM

Air-launched cruise missile

AGM-129 ACM

The AGM-129 ACM was the first stealth missile, but it was also problematic in service

 
 
Country of origin United States
Entered service 1990
Launch platform B-52H
Missile
Missile length 6.35 m
Missile diameter 0.7 m
Wing span 3.1 m
Missile weight 1 680 kg
Warhead weight 130 kg
Warhead type Nuclear, with a variable yield of 5 - 150 kT
Range of fire 3 000 km
CEP 30 - 90 m
Guidance TFR, INS and GPS

 

   The AGM-129 Advanced Cruise Missile (ACM) was the first cruise missile with full low-observability against radars, and was intended to be the replacement of the preceding AGM-86 ALCM. It is a significantly more technologically advanced weapon than its predecessor, and unlike the ALCM, the ACM was never adapted into a delivery system for conventional warheads.

   Development of a new cruise missile especially for the Advanced Technology Bomber (ATB), the ultimate product of this program was the B-2 Spirit, was initiated by the Defense Advanced Research Projects Agency (DARPA) in 1982, out of concern that launching the existing AGM-86B ALCM would reveal the ATB's position too easily. A "stealth bomber", DARPA reasoned, needed a "stealth missile" to be effective against the most advanced Soviet air defenses. A series of program dubbed Teal Dawn took place later that year, which devised a number of key technologies for use in the future cruise missile.

   It was quickly realized during the Teal Dawn study that maximizing the survivability of the ATB hinged more on keeping it as far from the target as possible than stealth features in the missile. To that end, a range of 11 000 km was called-for, no doubt to the chagrin of the US Air Force (USAF) (the whole point of the ATB had been to achieve surprise through radar stealth in order to drop gravity bombs directly over the target, in much the same manner as the B-1B Lancer was to employ supersonic speed, as the USAF had a strong and deep-rooted ideological bias against stand-off air-launched weapons; see the AGM-86B ALCM page for further background in this matter). Measures were also called-for to reduce the missile's infrared profile, due to the rapidly increasing quality and usage of Infra-Red Search and Track (IRST) sensors by the Soviet armed forces. As a result, a missile not significantly larger or heavier than the ALCM now had to fly over seven times as far, in addition to having the most advanced low-observability features yet devised; a daunting challenge to say the least.

   By 1983, the Teal Dawn concept split into two projects; one for the aforementioned 11 000 km stealth cruise missile, and another for a stealth cruise missile with a 3 000 km range. The rationale was that technology required to create the longer-ranged missile would require up to a decade to develop, while a missile with less than half the range was deemed possible by the mid-1980s. DARPA was satisfied with the Teal Dawn design formula by 1983, at which time LTV Aerospace was awarded a $12.1 million contract on January 17th of that year to develop the 11 000 km missile as the Long-Range Conventional Stand-off Weapon System (LRCSW), while a request for proposals was issued for the 3 000km missile, now dubbed the ACM, in September of 1982.

   At least three companies responded to the request for proposals; Boeing, Lockheed-Martin, and General Dynamics. On the rationale that the new missile had to be delivered as soon as possible (the ATB was then promised to be in widespread service by the late 1980s), the USAF selected the design proposal they evaluated as having the most potential, and decided to develop the ACM with very heavy concurrence (i.e., development, testing, production, and operational service were to overlap as much as possible). The General Dynamics proposal was announced as the winner on April of 1983, and a fixed-price cost incentive was placed upon the ACM program. The contract was for 1 500 missiles.

   Despite the USAF's much greater enthusiasm, funding, and unity (compared to the chaotic and divisive ALCM program in the 1970s) for the ACM program, it was still a painfully prolonged effort, and one which attracted increasingly wide and intense criticism. The first test flight took place in July of 1985, but numerous quality control problems and testing mishaps surfaced during further test flights. The testing of the ACM was further marred by a series of disputes between General Dynamics and the International Association of Machinists union, which reached a climax in 1987 in the form of a 3-week strike, further slowing the ACM program. The first production missiles were delivered to the USAF later in 1987, but due to its concurrency and ongoing problems, the ACM was still years away from becoming operational. In fact, the ACM's technical difficulties were only just beginning, as were its political difficulties.

   By the late 1980s, one of the ACM's most ferocious critics in Congress was the Chair of the House Armed Services Committee, Les Aspin. It was stated by Aspin in the press that out of the 8 strategic programs his committee was overseeing, the ACM had the worst problems and was "a procurement disaster". The status of the ACM program further soured Congress' opinion of the program over time, as its classification was increasingly abused by the Pentagon to conceal the system's problems from government oversight. As noted in Herbert N. Foerstal's book Secret Science (Praeger Publishers, 1993), Aspin noted in 1989 that "A report has been done, but because of the high classification, the report remains locked in the committee safe. The ACM is not classically a black program. I am not barred from acknowledging its existence. But it is protected in nearly all interesting details by high classification. There is only one interesting thing I can tell you. It is a procurement disaster. The ACM is the worst of all the programs the committee has to look at... why? Because of the classification, the reasons will have to remain sketchy, almost nonexistent." The fact that Aspin had become so critical of the ACM was especially telling, as he was a Democrat, and his party was the driving force in Congress for the very creation of the ATB and ACM. The Republicans advocated of the B-1, while Democrats fiercely opposed it and preferred stealth bombers and cruise missiles, both of which most Republicans vehemently opposed. Though largely forgotten today, the B-1 was inevitably known as the "Republican Bomber" and the B-2 as the "Democratic Bomber" for these reasons. The ACM's own political support base was now rapidly turning against it.

   The USAF eventually joined the list of parties dissatisfied with the ACM, and ordered all deliveries stopped in 1989 through 1991, pending numerous corrections of lingering quality control problems and performance shortfalls. During the same period, Congress forcibly defunded the ACM, and threatened to terminate the entire program if the manufacturer and subcontractors couldn't cough-up a cost-effective product. Another effort to reduce the cost and increase the quality of the ACM was the decision to hire a second major manufacturer, McDonnell Douglas Missile Systems, in May of 1988. In addition, the government of Canada granted the USAF's request to use Canadian airspace to conduct further flight trials for the ACM. It was intended that General Dynamics and McDonnell Douglas would offer increasingly better and cheaper product through competition, but McDonnell Douglas wasn't finally qualified to begin construction until 1990, and neither company by then had proven able to compete. This forced the USAF to drastically and expensively restructure the ACM program, and lengthen it considerably to accommodate its many delays. By 1991, it was decided to delay the competition until 1993. At some point by this time, the planned purchase of 1 460 missiles had been reduced to 1 000.

   However, by the end of 1991, two events outside the ACM program had occurred that each could easily have doomed it. The first was that the ATB had been proven even more problem and delayed, and it wasn't until July 17th 1989 that the first B-2 Spirit took to the air. This guaranteed that the ACM would become operational long before the B-2, so the USAF was forced to outfit the B-52 Stratofortress to use the ACM as an interim launch platform. The B-1 had been considered, but this aircraft was suffering problems stemming from a hyper-prolonged development as well, and the ACM was too long to fit inside the B-1's internal bays. The other event was the dissolution of the Soviet Union and the Warsaw Pact in 1991, which effectively robbed the ACM of the reason for its existence. With rapidly improving relations between the former Warsaw Pact nations and the West, and extensive commerce and diplomacy between the US and China, there were no plausible scenarios in which the AGM-129 ACM represented a valid solution. Its initial operational capability was announced in 1990, though significant hurdles remained.

   Perhaps owing to the out of control costs and problems of both the ACM and the B-2 (only one airframe was built for developmental purposes, and the production run ultimately capped at only 21 aircraft), the ACM ultimately never fulfilled its ultimate purpose --- to be integrated into the B-2. The B-52G was also used to carry it, but these were retired too soon to realize this plan, and the only aircraft ever made compatible with the ACM was the B-52H. Congress was still quite furious over the management of the ACM after the Cold War as well, and in 1992 legislation allowing for an addition $5.7 billion for the program in fiscal 1994-96, they stated rather bluntly on public record that this was a "bailout" for a USAF "fiasco." President George H.W. Bush announced in January of 1992 that ACM production would be terminated at 640 missiles, and no further ACMs would be purchased, which was also effectively the cancellation of the competition between General Dynamics and McDonnell Douglas. The USAF soon after halted their ACM purchases at only 460, ending the program's development phase even sooner. It also wasn't until 1992 that the ACM was declared fully-operational. McDonnell Douglas's missile division was ultimately sold to Raytheon, who eventually became the prime contractor.

   The appearance of the AGM-129 ACM is distinct. It has a long, cylindrical fuselage, a nose and tail that taper-down to an extremely sharp point, and a chined radome that gives the ACM a distinct chisel-like nose. The air inlet is located on the central underside of the missile, and is flat, conformal, and triangular in shape. Three small trapezoidal fins are located on the tail in a 90-degree pattern, with the central tailfin located on the underside. The wings are larger and longer than those in the ALCM or the Tomahawk, and when deployed have a unique negative (i.e., "swept-forward") layout. The horizontal fins also have a semi-negative orientation, with the leading edges at a 90-degree angle. Prior to launch, the fins are wrapped around the tail of the missile, and spring into their deployed form shortly after release, while the wings are recessed into a pair of slots in the aft section, and swing forward shortly after the engine starts.

   The overall composition of the ACM remains a closely-guarded secret, even now in the 21st century. Titanium and steel are used extensively in the engine, but the composition of the fuselage and wings (which is claimed to be radar-absorbent material) remain classified. The paint used on the exterior surfaces is also a radar-absorbent material compound, likely consisting of a ferrite base. The 2D shape of the thrust nozzle also greatly contributes to the missile's infrared stealth, as does the deep recession of the engine into the fuselage, and the use of a highly indirect air inlet system.

   The ACM is guided using the same Terain Contour Matching (TERCOM) and Inertial Navigation System (INS) guidance method as in the Tomahawk and ALCM, but instead of using the McDonnell Douglas AN/DPW-23 Terrain Following Radar (TFR) fitted to those missiles, the ACM is instead guided by a "Light Detection And Ranging" (LIDAR) set; this system operated on the same principles as radar, but using laser beams instead of radio waves). The key advantage of using LIDAR is that it can't be detected unless a laser receiver is directly below the missile, rendering it significantly more "stealthy" than a missile using TFR. This guidance is also said to be extremely precise, although the radar reflectivity problems that the TFR system used in the Tomahawk and ALCM likely have parallels with the LIDAR guidance used in the ACM. Namely, terrain that is exceptionally reflective or absorbent of light (sometimes seasonally, such as a lake that dries-out in summer, or freezes in winter) could be unrecognizable to LIDAR, and as there is no LIDAR terrain-mapping technology for creating "roadmaps" for use by the ACM, these would probably have to be programmed into the guidance system using a combination of satellite photographs and guesswork. The computer systems for the ACM were also exceptional for the 1980s, in that they integrated all control functions into a single "databus" computer; a practice now fairly common in guided missile development. The accuracy of the ACM is stated to be between 30 m and 90 m --- not that this is a significant difference when the nuclear warhead on board detonates.

   Further software and guidance upgrades for the ACM were planned from 1985 onward, in a DARPA program code-named "Thirsty Sabre", which would have given the ACM the ability to attack fleeting targets (such as batteries of mobile ballistic missile launchers). However, this effort was abandoned by the end of Operation Desert Storm in 1991, once it became clear that such enemies were far more elusive than the USAF had expected; e.g., no deployed mobile Scud launchers were ever found and destroyed.

   The engine that propels the ACM in flight is a Williams F112 turbofan engine. It is derived from the same F107 engine that powers the AGM-86 ALCM and the BGM-109 Tomahawk (the F112 was originally designated as the F107-WR-14A6, then later as the F107-WR-103). This engine produces 41% more thrust than the F107, and boasts a turbine blade cooling system that reduces the turbine inlet temperature from 1093°C to 954°C, and runs on the same Boron-Slurry JP-10 jet fuel as the F107. It is said that the efficiency stemming from the F112's improvements over the F107 are the secret to the ACM's greater range over the ALCM, but it is more plausible that the ACM simply carries more fuel, as improvements to the engine alone entail an improbable 50% increase in efficiency (even more improbable, in light of efficiency loss resulting from all of the cooling systems).

   The ACM flies at a speed of approximately 800 km/h, and can be programmed to fly at a variety of altitudes, depending on the required method of attack. Most commonly, it would fly very low at "nap of the earth" altitudes, sometimes weaving its way through steep vertical terrain as cover. The maximum range is widely-reported as about 3 000 km (some claim longer ranges, with one published figure being 3 400 km), but as with most other aspects of the ACM, the exact information remains classified.

   The only warhead carried by the ACM is a W80 nuclear 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. Most sources claim the ACM carried the W80-1 version.

   When not in use, the AGM-129 ACMs were stored inside special hardened shelters built especially for this purpose, which had a distinctive igloo-like design. These shelters also hold the pylons on which the ACMs are carried (which are commonly referred to as "packages"), and in practice, most were pre-loaded onto the pylons so that a B-52 may be outfitted with them as quickly as possible.

   The B-52H can carry up to 12 ACMs on two external pylons, or up to 8 internally on rotating launch racks. This allows a single B-52H to carry a grand total of 20 ACMs. Since the B-1 and B-2 were never outfitted to carry cruise missiles, the USAF's only option for attacking targets with these aircraft is to directly overfly them, and deliver free-fall ordnance. This would pose serious problems for an attack on a well-defended target, as the B-2 would be forced to reveal its presence and precise position in real time, well within the range of many air defense weapons on the ground. Similarly, the supersonic dash capability of a B-1 flying directly through an alerted air defense umbrella would offer no defense.

   A notable mishap involving an AGM-129 ACM occurred on December 10th 1997, during an exercise in which at least one missile was launched. While en-route to the target in the US Army's Dugway Proving Ground after flying for 3.5 hours, the ACM collided with two trailers belonging to a cosmic ray observatory owned by the University of Utah and Tokyo University. The observatory was located inside the proving ground's "hazardous operations" area, and its location was well-documented by the US military; as such, how the missile could have collided with the trailers is unclear (especially in light of the fact that even in "nap of the earth" flying, the ACM is supposed to fly high enough off the ground that it wouldn't hit an object that low, even if its presence was not anticipated).

   The ACM seemed to have troubles that followed it all the way into the 21st century. The USAF publicly stated in February 2006 that the ACM would remain in service until 2030, and that work was underway with the Department of Energy to develop an improved warhead for it. The USAF factsheet on the ACM dated August 2007 further reaffirmed that "The ACM is anticipated to remain in service until 2030". However, budget documentation released in February 2007 told a different story, that "The ACM fleet design service life expires between the years 2003 and 2008. .... FY08-13 funding was zeroed out for higher Air Force priorities". These were noted by John Pike's GlobalSecurity.org, who contacted several USAF officials for clarification, but received no response. However, in February of 2008, the USAF formally announced the decision to retire and destroy the entire ACM fleet, which was to be completed by 2013.

   Though despite the announcement of the decision to retire the ACM, Raytheon received a $5.76 million contract in 2009 for “AGM-129A ACM engineering services” --- a service life extension plan that factory rebuilt the doomed missile fleet to be able to serve into the 2030s. It was one of the last in a long line of blunders in the ACM program.

   However, the greatest blunder wasn't a developmental or program management gaffe, but a weapon handling accident. The bleakest moment in the AGM-129 ACM's career was August 30th 2007, when a B-52H carrying 12 ACMs with live nuclear warheads departed Minot AFB in North Dakota, and flew to Barksdale AFB in Louisiana, where the missiles were to be decommissioned. While this mission in and of itself was not unusual for USAF operations, it was certainly unusual that half of the ACMs were left loaded with live nuclear warheads by mistake. A series of negligent practices caused the mishandling to go unnoticed until long after the ACMs had arrived at Barksdale --- an unauthorized ordnance handling shortcut, and a failure of various logistics staff to communicate changes in the order and storage locations of missiles led the breakout team to send one of the wrong sets of 6 missiles to the tarmac; the transport crew towed the missiles to the bomber without either inspecting them, nor ensuring they had already been inspected (both actions are mandatory); the munitions control center did not verify as required either that the missiles had proper clearance to be loaded, nor that they were approved for pylon loading; while the B-52 now carrying the missiles was parked overnight at Minot, the detail of armed guards required to protect nuclear ordnance were not assigned as required; during pre-flight checks on the following morning, the instructor radar navigator only inspected the missiles on one of the two pylons, not both as required; the pilot did not do his own pre-flight inspection of the missiles as required, but logged all them as unarmed anyway; after landing at Barksdale, the bomber remained parked for 8 hours without the required security detail; and only as the missiles were being unloaded 36 hours after the transfer began did the Barksdale munitions crew notice that half of the "dummy" missiles were carrying live nuclear warheads. This was logged as a "Bent Spear" incident (i.e., a mishap involving a nuclear warhead that does not result in the warhead being lost or damaged), the first such incident to occur in the US military in some 40 years.

   By April of 2012, the last operable AGM-129 ACM was destroyed, ending its brief and colorful operational service. The ACM is to be replaced, along with the AGM-86B ALCM and AGM-86C/D CALCM, by a new air-launched cruise missile under the long-range stand off weapon program. The design and designation of this new missile have yet to be decided upon.

 

Variants

 

   AGM-129A: Basic production model, as outlined above. 461 were made.

   AGM-129B: Improved AGM-129A with structural and software improvements. Did not enter service.

   AGM-129C: Conventionally-armed AGM-129A. Did not enter service.

   Note: In addition, several sources such as Forecast international state that the AGM-129B was the conventionally-armed version, and make no reference to an AGM-129C. Other sources report there was indeed a planned AGM-129C, so several sources are in conflict with one another on the matter.

 

Similar missiles

 

   AGM-86B ALCM: The predecessor of the ACM, the ALCM has a reduced radar cross section design, but is not a "stealth" missile in the sense of being as undetectable as technologically possible. It also carries the same W80 nuclear warhead as the ACM, but has a shorter range of 2 400 km.

   AGM-109A Tomahawk: This is an air-launched version of the US Navy's ship-launched BGM-109A Tomahawk. It proved effective in testing, but was rejected in favor of the AGM-86B ALCM.

   LRCSW (or Long-Range Conventional Stand-off Weapon System): The other product of the Teal Dawn study, the LRCSW was to have almost four times the range of the ACM, effectively becoming an air-launched intercontinental stealth cruise missile. The program was terminated in 1991, and given the veil of secrecy that surrounded its efforts, it's unclear if any LRCSWs were ever built and test-launched.

   Taurus KEPD 350: A joint German-Swedish cruise missile, the KEPD 350 has a complex guidance system that employs image, GPS, and INS input, and a low radar cross section fuselage. However, it is nowhere near as stealthy as the ACM, carries a conventional payload, and has a much shorter range.

   Storm Shadow: This British-French-Italian air-launched cruise missile is similar to the KEPD 350, and has a low radar cross section fuselage.

   SOM: Yet another missile similar to the KEPD 350, the Tishich-made SOM also boasts stealth features and a fully-passive guidance system.

   HN-3: China's Hong Niao (HN) series cruise missiles are similar to the US-made BGM-109 Tomahawk, but the recent HN-3 is rumored to have a range of 3 000 km. If true, it is one of the few missiles to date which rivals the performance of the ACM, though the HN-3 is not a stealth missile.

   P-750 Meteorit: Called SS-NX-24 or Scorpion by the West, the Meteorit was another air-launched, nuclear-tipped cruise missile with a range of 3 000 km. Though while the ACM was to evade air defenses using stealth, the Meteorit was to bust-through using raw speed; it is believed to have had a top speed of over Mach 4 (4 940 km/h). This missile did not enter service.

   RK-55 Relief (Western reporting name SSC-X-4 or Slingshot): Theses nuclear-tipped Soviet cruise missiles, also had a 3 000 km range, though these missiles had no stealth features. The RK-55 Relief was launched by road-mobile vehicles. It was planned to enter service in 1987 but was banned under the Intermediate-Range Nuclear Forces Treaty.

   S-10 Granat (Western reporting name SS-N-21 or Sampson): another Soviet nuclear-tipped cruise missile with a 3 000 km range. The S-10 Granat was launched from the torpedo tubes of submarines. These missiles were reportedly converted to carry conventional warheads and are used by the Russian military to this day.

 

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AGM-129 ACM

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