The B-52 Almost Got An Ahead Of Its Time Air-Launched Ballistic Missile Named Skybolt

Air-launched ballistic missiles are back in vogue now, so it's worth remembering that the Air Force was looking to adopt one more than 50 years ago.

USAF

Interest in air-launched ballistic missiles has seen something of a renaissance around the world in recent years, notably in Russia, China, and Israel. At the same time, the U.S. Air Force is in the process of developing new, large, long-range, air-launched hypersonic weapons for its B-52 bombers that have similar general form factors to more traditional air-launched ballistic missile designs. However, the concept is nothing new and Air Force was planning to adopt a nuclear-tipped air-launched ballistic missile, known as the Skybolt, as a payload for its B-52s more than 50 years ago.

In 1959, the Douglas Aircraft company won the U.S. Air Force's first contract, worth $3 million at the time, or nearly $26.4 million today, to conduct an initial design study for Skybolt, which was originally known simply as Weapon System 138A, or WS-138A. Douglas subsequently subcontracted with Northrop, Aerojet, and General Electric to develop the guidance system, rocket motor, and reentry vehicle for the weapon, respectively.  

The Air Force had first begun laying the groundwork for Skybolt after the U.S. Navy began the development of the Polaris submarine-launched ballistic missile in 1956. There were fears within the former service that Polaris would obviate the need for strategic bombers, compounded by separate and growing concerns about the expanding capabilities and general density of Soviet air defenses.

In 1957, the Air Force had initiated its first foray into the development of an air-launched ballistic missile as part of the Weapon System 199 program, or WS-199. Under WS-199, in November 1958, a modified B-47 Stratojet bomber successfully launched an experimental air-launched ballistic missile test article called Bold Orion, which the Martin company had designed, for the first time. The next month, another B-47 fired a two-stage Bold Orion prototype. Days after that test, a B-58 Hustler bomber conducted the first launch a different prototype design from Convair and Lockheed, known as High Virgo. McDonnell also built a missile for WS-199, the Alpha Draco, but it was never air-launched.

A Bold Orion missile, an immediate predecessor to the Skybolt, mounted on a B-47 bomber.

High Virgo suffered a number of failures during testing between 1958 and 1959, largely due to its guidance and communications systems, and never flew farther than 310 miles, according to a report the Federation of American Scientists published in 2019. Bold Orion, however, successfully completed 11 of 12 test launches and the two-stage version demonstrated a maximum range of over 990 miles. 

The WS-138A program leveraged the experience gained during these experiments in the development of Skybolt, which the Air Force subsequently also designated GAM-87A. In February 1960, the Air Force authorized another $32 million, or around $281.1 million today's dollars, for Douglas to move beyond the design stage and actually begin building prototype weapons.

Douglas' final Skybolt design was a two-stage ballistic missile, similar in broad concept to the Bold Orion. The weapon was more than 38 feet long with its aerodynamic tail cap and 35 inches in diameter. This actually made it shorter than North American's GAM-77A Hound Dog air-launched cruise missile, which the Air Force had already put into service in 1960 as an interim standoff weapon for the B-52 ahead of the introduction of the GAM-87A.

After launch, the GAM-87A's tail cap would fall away and the first stage rocket motor would ignite, boosting it into a ballistic trajectory. That stage would then fall away and the second stage would take over with rocket motor with "a gimballed nozzle allowing it to maneuver in the upper reaches of the atmosphere and the vacuum of space where control surfaces cannot function," according to the Federation of American Scientists' report. An inertial guidance system would steer the weapon toward the target.

The GAM-87A's primary armament was originally going to be single W47 thermonuclear warhead, the same one used on Polaris, but this was eventually changed to a W59, the same warhead on the Minuteman silo-launched intercontinental ballistic missile. The Air Force's desired maximum range for Skybolt was approximately 1,150 miles, with an apogee around 300 miles high.

Reaching a peak speed of Mach 15, the missile would have been able to cover this distance in just 12 minutes, according to the Federation of American Scientists. The weapon's range and speed would have allowed B-52s to strike deep into Soviet territory, while also reducing the bombers' vulnerability to hostile fighter jets and surface-to-air missiles. Being able to strike quickly and from multiple and unpredictable vectors at once offered significant advantages over ground-based ballistic missiles in fixed emplacements or silos. This was also true of the submarine-launched Polaris.

The United Kingdom, which was facing similar concerns about the vulnerability of its strategic bombers, had asked to and was allowed to join the Skybolt program in 1960. The Avro Vulcan, one of the Royal Air Force's three so-called "V bombers," the others being the Handley Page Victor and the Vickers Valiant, was chosen to be the primary launch platform. The Victor and a modified Vickers VC10 airliner, which the Royal Air Force also operated as an aerial refueling tanker, were also considered as possible GAM-87A carriers, according to V Force – The History of Britain's Airborne Deterrent.

However, despite the clear interest and commitment of both the U.S. Air Force and the U.K. Royal Air Force, Skybolt quickly ran into technical difficulties and setbacks. In 1959, the Air Force had already canceled work on a more powerful B-58B Hustler variant, which was initially expected to be the primary launch platform for the GAM-87A, shifting focus to integrating the weapon on the B-52. Beyond the missile itself, Douglas needed to develop a new, specialized heavyweight pylon so the B-52 could carry two Skybolts under each wing, as well as loading equipment large enough to handle the weapons.

Douglas

A schematic of the special wing pylon for the B-52, which could carry two Skybolt missiles.

Douglas

The special trailing for positioning two missiles underneath the pylon in order to load them, with an operator shown giving a sense of the scale of the system.

The Skybolt "program office asserted [the weapon] was 'the most complex ballistic missile system ever to be developed by the United States' due to the difficulty of launching the missile from a moving platform, the need to integrate the missile with the aircraft to in order to know its launch position precisely, and the need to operate in environments that could subject the missile to shock, vibrations, and rapidly changing conditions," according to the Federation of American Scientists. "President Kennedy himself even stated that the system was 'the most sophisticated weapon imaginable,' involving 'the kind of engineering that’s been beyond us.'"

The first five flight tests failed in some fashion or another. In the first test in January 1962, the second-stage motor failed to ignite and the first-stage motor didn't work in the second attempt. An electrical failure scuttled the third test and a data link failed during the fourth launch, precluding the collection of telemetry data to determine whether the missile had performed as intended. The fifth test launch, the first to actually involve a missile with a functioning guidance system, experienced failures with the weapon's gas generator and hydraulic subsystem "causing flight to end prematurely," according to an official, now-declassified internal Air Force history.

The sixth launch, which took place on Dec. 22, 1962, was successful, but only saw the weapon fly out to a range of 800 miles, 350 miles short of the Air Force's desired maximum range. By that point, under the new U.S.-military wide designation system that had gone into effect that year, Skybolt had gotten redesignated from GAM-87A to AGM-48A.

Faced with the prospect of rising costs, including more than $1 billion in 1960s dollars to buy over one thousand of the missiles, and delays, then-Secretary of Defense Robert McNamara killed the program the very next day. He also said he felt that air-launched ballistic missiles offered "no unique capability," especially over Polaris. By the end of the month, the Air Force had stopped all work on Skybolt.

This quickly caused a crisis with the United Kingdom, which had canceled its own Blue Streak nuclear-armed air-launched ballistic missile program, as well as plans for an upgraded Blue Steel II standoff missile in favor of Skybolt. The country had also decided to begin retiring its American-supplied Thor ground-launched intermediate-range ballistic missiles. Skybolt was to form the core of the U.K.'s nuclear deterrent capabilities for years to come. The U.S. government subsequently agreed to supply Polaris missiles, which the Royal Navy would employ from its new Resolution class ballistic missile submarines.

For the Air Force, the decision was certainly a rebuke, but the impact was decidedly less extreme. The service did still have the Hound Dog, by that point redesignated the AGM-28A, which would remain in service until 1976. Despite McNamara's dismissal of the air-launched ballistic missile as a basic concept and his clear support for Polaris, strategic bombers never went away. In the 1970s, the B-52 also gained a new nuclear missile, the AGM-69A Short Range Attack Missile (SRAM), as well, to help reduce its vulnerability to hostile air defenses. 

Had the time come, Air Force B-52s would have flown to their targets, at low levels to help further mask their approach, attacking air defense sites with SRAMs along the way. You can read more about the AGM-69A in this past War Zone piece. This eventually gave way to more modern air-launched cruise missiles, such as the AGM-86B and AGM-129 Air-Launched Cruise Missile. At present, the AGM-86B is the only nuclear weapon the B-52 is authorized to carry, though it is expected to gain a new stealthy air-launched and nuclear-armed cruise missile in the coming years.

The U.S. military did briefly return to the air-launched ballistic missile concept in the early 1970s, going so far as to conduct a successful test involving the launch of an LGM-30 Minuteman intercontinental ballistic missile, typically fired from a silo, from a C-5 Galaxy transport aircraft over the Pacific Ocean in 1974. The launch concept involved releasing the missile out of the back of the massive airlifter, after which a set of parachute oriented the missile into a near-vertical launch position. The missile's main rocket motor then fired, carrying it to an apogee of 20,000 feet, before it fell into the sea below. 

The United States ultimately abandoned its air-launched Minuteman plans for good during negotiations with the Soviet Union over the Strategic Arms Limitation Talks (SALT) treaty. However, the U.S. military has continued to use a similar procedure to launch ballistic missile surrogates from C-17 airlifters in support of missile defense system tests.

As it stands now, the B-52 is still set to become a major launch platform for oversized weapons once again, but, at least for the moment, the plan is for these to have conventional warheads. Last year, one of these bombers conducted its first flight with a test article being used in the development of the AGM-183A Air-launched Rapid Response Weapon, or ARRW. This weapon looks very much like an air-launched ballistic missile, but has a hypersonic boost-glide vehicle as a payload that is capable of maneuvering inside the atmosphere at extreme speeds. The Air Force is looking to integrate other boost-glide vehicles, as well as air-breathing hypersonic missiles onto the B-52 in the future and is in the process of developing new heavyweight pylons to better accommodate these and other very large weapons in the future.

Other countries have also been seizing on the concept and have put their own weapons into service, or appear to be getting close to that goal. Russia says it has deployed a limited number of Kh-47M2 Kinzhal air-launched ballistic missiles, a derivative of the ground-launched Iskander-M, as well as modified MiG-31K aircraft to launch them. China has also shown off its H-6N bomber, which is specifically designed to carry oversized payloads, possibly including the DF-21D air-launched ballistic missile and the WZ-8 high-speed reconnaissance drone. Companies in Israel are developing Rampage and Rocks, which are smaller air-launched ballistic missiles intended for fighter jet-sized aircraft.

So, more than five decades after Skybolt's inglorious end, not only has the B-52 endured, the Air Force is now closer than ever to actually fielding similarly large, long-range weapons that use rocket boosters on the bombers. Other countries are now moving in the same direction, showing that Douglas' air-launched ballistic missile was, in many ways, ahead of its time.

Contact the author: joe@thedrive.com