The AGM-129 ACM is an air-launched cruise missile acquired and deployed by the United States Air Force. It was built by what was originally General Dynamics Convair, an organization which during the life of the missile changed hands several times before becoming part of Raytheon Missile Systems. It was intended as a successor to the original USAF AGM-86 ALCM. This missile is a true product of the Cold War, having been the result of a requirement originally produced by the Air Force in 1982.

The development of this missile is another step in a long arms race of offense/defense involving strategic bombing which (if you want to be pedantic about it) can really be traced all the way back to the Zeppelin. Since I am pedantic, I will. You can skip this part if it bores you, of course.

The Zeppelin (and its contemporary the Gotha) were really the first 'strategic bombers' used in high-style warfare. They began the long seesaw between strategic attack and defense involving aerial bombardment. As the Zeppelin and Gotha began to range over British cities during World War I, they provoked the development of several methods of defense. Most well known was of course the interceptor aircraft; formerly-unarmed biplanes acquired teeth in order to attack and destroy Zeppelins and Gothas in the air. This was not an uneven match; Zeppelins and Gothas could carry lots of light machine guns, and aircraft of the day were quite vulnerable to light machine guns. Eventually, however, it became clear that the fighters could indeed take down their targets - assuming they could find them.

Initially, this of course simply meant using the Mk. 1 eyeball to search for targets. But with the advent of night bombing, even that became problematic. Plus, it was considered advantageous for the defenders to shoot down the bombers before they reached their targets. All manner of means of detection and tracking were invented, ranging from the arc spotlight (meant to locate aircraft at night and point them out to defenses) to the sound locator. Both were used in World War II and beyond. Anti-aircraft artillery was invented to engage these intruders from the ground.

In response to these measures, in World War II the U.S. Army Air Force (later USAF) pursued the notion of a bomber which could fly high enough and fast enough to make both detection and interception extremely difficult, and make engagement by AAA impossible. This was achieved with the first modern strategic bomber, the B-29 Superfortress - a pressurized, high-power, high-speed aircraft which delivered the first modern "strategic weapons" over Hiroshima and Nagasaki. The success of this system led to the (over)confident dictum that "The bomber will always get through" - and the USAF set out to build more and more modern, high-altitude, high-speed bombers. The trend continued, in the U.S., through the B-36 Peacemaker, the supersonic B-58 Hustler, and the high-capacity B-52 Stratofortress and the built-but-never-deployed supersonic B-70 Valkyrie.

The defense wasn't standing still, however. The USSR continued to develop ever more capable interceptors and invested heavily in the new technology of the Surface-to-Air Missile. Eventually, the U-2 Incident proved beyond a doubt that Soviet SAMs were capable of hitting even the most high-flying bombers. The B-70 and A-12 Oxcart/SR-71 Blackbird could still defeat missiles by outflying them (probably) but it was clear that the notion of altitude and speed as a shield was dying. In response, the USAF went the other way. Cancelling the B-70, they instead concentrated on bombers which could fly close to the earth. The B-1B Lancer, originally a supersonic replacement for the B-52, instead was repurposed to become a maneuverable, low-altitude bomber which could 'penetrate' enemy air defenses by flying low enough to hide behind terrain features. Radar can't see through the earth, and low-flying aircraft can remain below the horizon of radar sites if they choose their course carefully. If they do so, then it is very difficult to detect them unless they fly close to you, and very difficult to track them for long enough to engage them with missiles or vectored interceptors.

The problem was that a large portion of USAF offensive bomber strength was still made up of B-52s. Based on the same general design as the Boeing 707, this airplane is not designed for the violent maneuvering of terrain following. The USAF was quite eager to ensure that these aircraft would still be useful. Enter the cruise missile! It was reasoned that even if the bomber couldn't enter the enemy's defended airspace and reach its targets, maybe it could still be useful. The original ALCM was the answer to this problem. The B-52 was retasked with ferrying ALCMs to the edge of the Soviet air defenses, and then launching them at targets inside the Soviet Union. The cruise missiles, being small, maneuverable and patient, would then fly low and slow across Soviet turf, avoiding air defenses, and then strike the targets while the B-52 remained safely outside the defense perimeter.

This was all well and good for a time. However, as "look-down" radar systems came into widespread use in the 1970s and 1980s, it became clear to the USAF that its original cruise missile (the aforementioned AGM-86) was becoming more and more vulnerable to air defense systems. With look-down radar available to the USSR's defense forces aboard such interceptors as the MiG-31 Foxhound, which deployed in 1975, cruise missiles suddenly became viable targets. This tilted the balance in the Bomber race to the defense, and the USAF naturally began to look around for an edge to get them back in the game.

At around this time, "low-observability" technology was just coming into vogue (also known as 'stealth'). The F-117 Nighthawk and the B-2 Spirit were on the drawing boards. The USAF reasoned that one way to restore the viability of cruise missiles would be to make them stealthy, which should be easier given how small they were. And lo, the AGM-129 ACM (Advanced Cruise Missile) was born. Here's what it eventually looked like, courtesy of the USAF. The requirements of stealth ended up making it look somewhat peculiar to experienced planespotters - the wings are reverse-swept, and the vertical stabilizer is beneath the fuselage, making it look like it's flying upside down and slightly backwards.

It was intended for deployment on the same platforms as the AGM-86 - namely, the B-52 and the B-1B. A B-52 was able to carry up to 12 of them on pylons, three missiles clustered per pylon, or carry 8 of them internally in its bomb bay Common Strategic Rotary Launcher. It used essentially the same types of systems - Inertial Navigation Systems and TERCOM (albeit using LIDAR for its TERCOM measurements). It carried the W-80 mod 1 nuclear warhead, with a maximum yield of around 120 kilotons. The first AGM-129 was delivered in 1985, and it was first deployed in 1990. Originally, the plan was to build over 1500 of them to entirely replace the AGM-86 inventory; however, as the initial deliveries of the missile proved to have several defects, deliveries were halted on several occasions until the weapons could be made good. The number ordered continued to drop, eventually culminating in a final total of 460 missiles. As a result, the AGM-86 was kept in service; the stealth(ier) AGM-129 was reserved for use against more heavily defended targets.

Eventually, the AGM-129 would become (in)famous via its decommissioning, not its acquisition or use. On August 30 of 2007, as the USAF was ferrying AGM-129s from their deployed sites to Barksdale Air Force Base in Louisiana for decommissioning, six live nuclear warheads were accidentally left on six of the missiles, and their whereabouts not recorded. As a result, the originating base (Minot Air Force Base in Minnesota) effectively 'lost track' of the six warheads - an event known in the Nuclear Safety world as a BENT SPEAR (short cousin to BROKEN ARROW). There was a public outcry, and a highly-public investigation, as a result of which several highly-placed USAF officers lost their careers.

At present, the USAF claims (via its website) that the AGM-129 will remain in service 'through 2030', despite earlier reporting that the weapons would *all* be decommissioned in order to comply with recent arms control treaties. Air Force Magazine notes, however, that "The Defense Department is retiring the nuclear-armed AGM-129 ACM entirely." This is in order to comply with 2002 Moscow Treaty limits, under which the total number of nuclear weapons deployed by the U.S. bomber fleet was to go down to 528 - a number which could be met entirely with the older but cheaper-to-maintain AGM-86B. Since the AGM-129 was only ever a nuclear platform, it looks like it will be retired entirely.

Any time a nuclear weapon system is removed from the board without ever having been used, it can be looked at as a small victory for humanity.

AGM-129 Advanced Cruise Missile

  • Deployed: 1990
  • Contractor: Raytheon Missile Systems
  • Power plant: 1 turbofan engine
  • Thrust: ~730 lbs.
  • Speed: ~500 knots
  • Range: ~2,000 nautical miles
  • Guidance: Inertial navigation, TERCOM with LIDAR
  • Dimensions: 20'10" long, wingspan 10'2", more than 3,500 lbs
  • Warhead: W-80-1 selectable yield, max. 120 kt.

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