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AGM-69 SRAM

Air-launched ballistic missile

AGM-69 SRAM

During the 1970s and 1980s the AGM-69 SRAM was the primary tactical nuclear weapon of the US Air Force

 
 
Country of origin United States
Entered service 1972
Missile
Missile length 4.83 m
Missile diameter 0.44 m
Fin span 0.76 m
Missile launch weight 1 010 kg
Warhead weight ?
Warhead type Nuclear, up to 217 kT
Range of fire 169 km
CEP 430 m
Guidance Inertial navigation system
Launch platforms B-52, FB-111, B-1B

 

   One of the most iconic US nuclear munitions of the Cold War, the Boeing AGM-69 SRAM (Short-Range Attack Missile) was for some 20 years the primary USAF strategic deterrent. This missile boasted considerable performance, a strong yield, and some of the first stealth technology ever applied to a guided missile, but it was a troubled and dangerous device throughout its entire service life.

   The origins of the SRAM are rooted in a crisis the USAF experienced in the late 1950s, during which they finally began to appreciate the threat that Soviet Surface-to-Air Missiles (SAMs) posed to the bombers of the USAF's Strategic Air Command. The S-55 Berkut (reporting name SA-1 or Guild) had been in service for some time at that point, but the vastly more numerous S-75 Dvina (reporting name SA-2 or Guideline) posed a much more serious problem. As far as the USAF was concerned, a bomber that entered a SAM umbrella was as good as dead. To that end, development of a nuclear-tipped missile that could be launched from bombers gained a new priority, as these would allow the attacking aircraft to either destroy the target without coming within range of the SAMs, or even to destroy the SAM sites themselves.

   The initial approach was the latter, with first attempt at creating such a missile was the Northrop GAM-67 Crossbow. An anti-radiation missile with a conventional warhead, the Crossbow was bulky, and lacked the speed necessary to get ahead of the bomber launching it before it ran out of fuel; the USAF deemed it a failure, and only 14 Crossbows were built. A proposed supersonic version, the Longbow, never even proceeded as far as its predecessor.

   The USAF next tried to develop a missile that could bypass SAM umbrellas entirely, in order to attack targets on the other side (which would also allow bombers to attack the missile sites themselves). This next effort was to develop an air-launched ballistic missile, the GAM-87 Skybolt, but this weapon also proved unsuccessful. The eventual cancellation of the Skybolt in November of 1962 triggered a crisis in both the USAF and RAF (who had also planned to adopt this missile), as higher authorities in the government instead instructed the USAF to adopt the LGM-30 Minuteman intercontinental ballistic missile instead, while the RAF's nuclear deterrent role was eliminated altogether in favor of using Royal Navy ballistic missile submarines only. The USAF feared the same would happen to their own nuclear capability, so it should come as no surprise that they tried again almost exactly a year later.

   The USAF had fortunately developed a missile intended to serve as an interim for the Skybolt, in the form of the Boeing B-77 (later GAM-77, and finally AGM-28) Hound Dog cruise missile, which had already been in service since 1960. This large, airplane-like weapon could be launched from a B-52, flew at a speed of over Mach 2 (2 470 km/h), carried a nuclear warhead, and boasted a range in excess of 1 200 km. However, the Hound Dog's immense performance was offset by its immense size and weight. The B-52 Stratofortress could only carry them externally, and only had enough space for two of them. It was decided that a newer, smaller missile was still needed.

   On November 23rd 1963, Strategic Air Command began a series of design studies for such a weapon, culminating in the establishment of an official requirement in March of 1964, designated Specific Operational Requirement 212. The Office of the Secretary of Defense accepted of the proposal, and SecDef Robert S. McNamara officially approved the program on March 23rd 1965. On October 31st 1966, Headquarters Air Force contracted the Boeing Company to develop and produce the new missile. The system was named the SRAM, and assigned the ZAGM-69 designation number.

   Though while achieving funding and endorsement for the SRAM proved relatively easy, actually building the missile that Boeing proposed proved a much more complicated matter. The solid fuel rocket propulsion technology in the class required for the SRAM was still in its infancy even in the late 1950s, and the propellant failed to meet the USAF's requirements for safety, stability, and self life.

   The schedule slipped by over two years, and the first test launch didn't take place until July 29th 1969. The program assured Congress that the problems with the fuel would be fixed within a few years, but they were destined to remain mostly unresolved for decades. Production finally began in October of 1970, but deliveries didn't begin until March of 1972.

   The SRAM promised to drastically improve the standoff nuclear attack capabilities of Strategic Air Command's bombers. The AGM-28 Hound Dog cruise missile it replaced had been a huge and ponderous weapon that was very conspicuous (and thus easily detected and shot-down). A B-52 Stratofortress could only carry two Hound Dogs, both of which had to be mounted externally under the wings, which also created tremendous drag. By contrast, the SRAM was several-times smaller and lighter, and enormously faster, enabling a B-52 to carry 8 of them internally and attack from a greater distance. The B-52 could also carry an additional 6 SRAMs (for a total of 12) in a pair of 3-missile clusters under its wings, at a substantially lower penalty in weight and drag compared to a pair of Hound Dogs.

   The FB-111A Aardvark and B-1B Lancer were also able to carry SRAM. The FB-111A carried less (2 internally and 4 externally, for a total of 6), while the B-1B carried more (three rotary launch racks with an 8-round capacity, for a total of 24). The arrival of the SRAM was even more critical for these aircraft, as they were unable to carry ordnance as large as the Hound Dog.

   The AGM-69 SRAM has a simple appearance, with a long cylindrical fuselage, a nosecone that tapers down to a fine point, and a boat tail at the aft end. Three small rectangular fins are located aft, in a triangular pattern. A narrow strip along the topside of the fuselage holds both the lifting eyes used to mount the SRAM on a pylon, and wiring pathways. The rocket motor sports a single small thrust nozzle.

   Little information has been published on the composition of the SRAM, though a 1975 USAF report on the missile reveals that its rocket motor is made of steel.

   The SRAM is also notable for being one of the first missiles ever constructed with radar-defeating features, though it isn't as stealthy as many subsequent tactical missiles. Almost the entire fuselage if coated by a 20 mm thick rubber-based compound, while the fin assembly was made of phenolic material, all of which are substantially absorbent of radio waves. Combined with the SRAM's blistering speed and minimal radio emissions, this significantly reduced its chances of being detected and tracked, let alone successfully engaged.

   Propulsion for the SRAM is provided by a Lockheed-Martin Lockheed SR75-LP-1 solid-fuel rocket motor. The fuel in the aft cell of the combustion chamber effectively forms the boost stage, which accelerates the missile to its full speed in a matter of seconds, and is totally expended in the process. The forward cell contains a slower-burning fuel that forms the sustainer stage, and propels the SRAM throughout most of the remainder of its flight

   The performance of the SRAM is staggering, even by 21st century standards. It flew at a speed of up to Mach 3 (3 700 km/h), and out to ranges of 56 km to 169 km, depending on the programmed flight profile. This allowed a bomber to attack from far outside the effective range of nearly all Cold War-era air defense systems, and left the enemy very little time to react, and a fiendishly difficult target to hit (not even considering the SRAM's stealth features) even if they could fire upon it in time.

   The guidance system of the SRAM is the General Precision/Kearfott KT-76 inertial measurement unit, a type of inertial navigation system. While such guidance systems are notoriously imprecise, they carry two very strong advantages for a missile like the SRAM; The guidance system is completely passive, with no detectable emissions, and effectively impossible to jam or misdirect. However, the SRAM does emit radio waves, as a Stewart-Warner radar altimeter is used to gauge its altitude. It is probable that the radar altimeter could be jammed, though unless the SRAM was flying through steep and complex vertical terrain (e.g., a mountain range), this would have little effect on the missile's accuracy. These systems are collectively controlled by a Delco 2 000-word computer (after modernizations, the Delco computer had a 8 000-word capability).

   The accuracy of the SRAM is rather poor compared to most conventionally-armed air-to-ground missiles, with a circular error (CEP) of 430m. Though granted, CEP only determines the grouping of half of a given set of projectiles fired (the other half are omitted from the figure), and has no bearing on where the intended target is located, but it matters little in the case of a weapon with a yield of up to 210 kT; as the old saying goes, "Close only counts in horseshoes and nuclear weapons".

   Perhaps the most interesting aspect of the SRAM's guidance is that it can be programmed to perform a single, very sharp turn shortly after launch. This can even be a 180-degree "U-turn", allowing a bomber to attack a target behind it. This gives the launch aircraft an element of surprise, as it can attack a target off its course, or even launch a missile against an enemy as it withdraws (a high-technology "Parthian Shot"). In short, aircraft carrying the SRAM can attack anything around them in any direction, without changing course, which presents many tactical advantages.

   The SRAM is often mistaken for a cruise missile, given its range, but its trajectory is actually that of a ballistic missile (much like the ill-fated Skybolt). Upon launch, the missile either flies into a steep arc and plunges down onto the target from high above, or when programmed to fly straight ahead, it will do so briefly on thrust and inertia before beginning its descent.

   The only warhead used in the SRAM was the W69, a nuclear warhead with a variable yield. The aircrew launching the missile could remotely program the W69 during a mission and prior to launch, with the lowest setting at 17 kT, and the highest at 217 kT. The W69 is essentially a hydrogen bomb, whose higher yield settings are produced by creating nuclear fusion in the fissile core during detonation. The lower-yield settings are achieved by disabling the mechanisms that create nuclear fusion, resulting in a fission reaction instead. As such, these types of munitions are often referred-to as "fission-fusion" warheads.

   The AGM-69 SRAM ultimately served two decades in the USAF, during which it was the primary nuclear weapon in Strategic Air Command's corner of the Pentagon's "Nuclear Triad". However, despite the SRAM's importance, its long-standing problems that had been "swept under the rug" continued to plague the missile throughout its career.

   The first test launch of an operational SRAM didn't occur on August 20th 1974, and it ended in failure. While no subsequent test launches of the SRAM, the final launch of an operational SRAM took place on July 26th 1983; meaning, no SRAMs were test-launched during almost the entire latter half of their service life.

   A special variant of the SRAM for the B-1A Excalibur bomber was planned throughout the 1970s as well, but this missile (the AGM-69B) was canceled along with the B-1A bomber. The AGM-86A ALCM was initially intended to succeed the canceled AGM-69B, but this too was canceled soon after the B-1A, and the larger AGM-86B variant replaced it in development. The later B-1B Lancer was briefly compatible with the SRAM, though the latter was retired soon after, and none of the other ALCMs were integrated into the B-1B either.

   Possibly the worst moment in the history of the SRAM occurred on September 15th 1980, when the right wing of a B-52H parked on the alert apron at Grand Forks air force base caught fire. The fire was contained on the wing and extinguished, but had the crosswind not been blowing away from the fuselage, experts contended, it would likely have entered the bomb bay --- which contained live SRAMs. A nuclear detonation would not have occurred, but the volatile nature of the solid rocket motor propellant was another matter.

   The W69 warhead itself was also found to be vulnerable to fire. If exposed to open flame, it was possible for the conventional explosives inside to combust or even spontaneously detonate, depending on the circumstances. Officially, a cooked-off W69 would not successfully produce a nuclear chain reaction (fortunately, the USAF never had to find out the hard way), though the resulting plume of pulverized plutonium still represented a serious radiation hazard. Moreover, the toxicity of plutonium is far more dangerous than even its radioactivity.

   The end of the SRAM's operational service was also decidedly ignominious. Mounting concerns of the weapon's safety margins accumulated throughout the 1980s, beginning with the aforementioned September 1980 ground fire, and Boeing's now two-decade-long failure to make good on their promise for improved reliability and safety. As a result, SecDef Richard "Dick" Cheney ordered the entire SRAM inventory grounded in June of 1990, pending the completion of an investigation into the missile's problems. The outcome showed that the SRAM's problems were not only dire, but also unfixable, and worsening every year. This led to the termination of the entire SRAM inventory in 1993.

   Production of the SRAM lasted only 5 years, but during that time a total of 1 541 SRAMs were produced, including 41 developmental missiles (which were, for all intents and purposes, prototypes). The tooling, jigs, and other equipment needed to produce more was retained at USAF Plant #77 in the event that further orders were placed, and an option for another 45 missiles was initially offered, but no further operational SRAMs were produced. According to Forecast International, each had a unit cost of over $740 000 in 1975 US dollars.

   No SRAMs have been produced since the 1970s, and the support and spare parts infrastructure for them was terminated in 1991, along with all the factory tooling and documentation required to produce more. Furthermore, in accordance with arms reduction protocols, every SRAM in the US inventory was either destroyed or rendered inoperable for display purposes. The W69 warheads removed from the SRAMs were put into storage, and some of these were later installed in B-66 free-fall nuclear bombs.

   As such, the AGM-69 SRAM is effectively an extinct weapon system --- an altogether surprising fate, considering that the B-1 and B-52 bombers meant to carry it are both still operational.

 

Variants

 

   AGM-69 SRAM: Designation of the initial design; following testing, no production AGM-69s were forthcoming.

   AGM-69A SRAM: The basic production model, as described above.

   AGM-69B SRAM: This was an improved AGM-69A with a new guidance system, motor, and warhead, which was intended for use in the B-1A Excalibur bomber. When President Jimmy Carter terminated the B-1A in 1978, the AGM-69B program was terminated with it, and none of these missiles were ever delivered. The B-1 program later produced the B-1B Lancer in later years, but this bomber used standard AGM-69As, and no later models of this missile were forthcoming.

   AGM-131 SRAM II: More of a new design than an actual derivative, the AGM-131 SRAM II was proposed as the successor to the SRAM. Due to rapidly-shifting defense politics and budgetary priorities at the end of the Cold War, this program was terminated in 1991 by President George Bush, and no AGM-131 SRAM IIs were ever constructed.

   SRAM-L: A proposed extended-range version of the AGM-69 design with radically-increased electronic counter-countermeasure capability, the SRAM-L was offered by Boeing to the USAF in the early 1980s. It was rejected by the USAF, as it was found to conflict with their already ongoing ASALM (Advanced Strategic Air-Launched Missile) program.

   ASAT: The most unusual SRAM variant, the LTV ASAT missile was partially derived from the AGM-69 SRAM. This air-launched missile was designed to be launched from a fighter, and shoot-down satellites. Though ultimately, this missile was never accepted into service either.

   SRAM/LEAP: This was a proposed air-launched anti-ballistic missile, based on the SRAM (LEAP is short for "Low-Exo-Atmospheric Projectile"). The program was terminated before any could be built.

   A conventionally-armed version of the SRAM was proposed as well (which apparently never received an official designation), but due to the poor accuracy of the nuclear version, no conventional SRAMs were produced.

 

Similar weapons

 

   Blue Steel: This British tactical missile was the spiritual predecessor of the AGM-69 SRAM. Everything about this missile was shocking; it weighed over 3 100 kg, carried a 680 kg thermonuclear warhead with a multi-megaton yield, was carried in pairs and launched from the famed V-Bombers, boasted a range of 925 km, and covered that distance at 2 840 km/h (Mach 2.3) (a decidedly much more impressive feat than 80 km at 4 320 km/h (Mach 3.5)). The existence of an operational missile like this one would create quite a panic even in the 21st century, but the Blue Steel entered service way back in the 1950s. Due to rapidly shifting strategic priorities in the UK government, the Blue Steel was retired without replacement after only a decade of service.

   GAM-47 Skybolt: The Skybolt was a technological marvel, with three times the speed and ten times the range of the SRAM --- when it worked. Poor reliability, cost and schedule overruns, and disagreements between the US and UK governments over this missile ultimately led to its cancellation.

   Minuteman 1B: Though not technically an air-launched ballistic missile, the USAF demonstrated that the Minuteman ICBM could be dropped from a C-5 Galaxy and launched in mid-air during its descent. However, it proved a significant technical challenge, and coupled with the then-upcoming SALT negotiations, further development was not pursued.

   ASMP: The French counterpart of the SRAM, the Aérospatiale ASMP (Air-Sol Moyenne Portée) boasts a comparable speed and yield to the SRAM, but with two critical differences. It has three times the range, and is a cruise missile rather than a ballistic missile. The ASMP is used only by France.

   Kh-15: Developed in response to the SRAM, the Raduga Kh-15 (code-named AS-16 or Kickback by the West) could be said to be the missile that achieved everything that slipped away from the SRAM. Another air-launched ballistic missile, the Kh-15 is launched from a much wider range of aircraft, it's almost twice as fast, the range is claimed to be three times as long, and it has conventionally-armed versions as well as nuclear versions. This missile is also still in service as of mid-2018, and is used only by Russia.

   Kh-47M2 Kinzhal: The newest air-launched ballistic missile, the Kinzhal ("Dagger") is claimed to have a Mach 10 speed (around 12 000 km/h), a range of over 2 000 km, a nuclear payload, and quasi-ballistic maneuvering capabilities on descent. However Western observers have expressed skepticism toward its capabilities. This missile is used operationally since 2018 on MiG-31K long-range multi-role fighters. NATO currently has no codename for this missile.

 

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