In the late 1950s, the US military and scientists developed and tested two experimental air-launched ballistic missiles. The products of the WS-199 program proved the fundamental possibility of creating such a weapon, but their own characteristics were far from desired. For this reason, the Bold Orion and High Virgo projects were closed, and based on their developments, they began to design a new rocket. At different times, this weapon from the Douglas company was named WS-138A, GAM-87, AGM-48 and Skybolt.
In the second half of the fifties, the US Air Force faced some difficulties in the field of intercontinental ballistic missiles, which forced them to pay more attention to aviation weapons. Within the framework of the Weapon System 199 program, two promising aeroballistic missiles were created for existing bombers. However, the flight range of the WS-199B Bold Orion and WS-199C High Virgo products was 1100 and 300 km, respectively - less than was required to effectively solve combat missions and defeat targets in the territory of a potential enemy covered by powerful air defense.
Rocket WS-138A / GAM-87 on a transport trolley. Photo by US Air Force
By the beginning of the sixties, the Air Force command, having seen the results obtained, decided to abandon experimental samples in favor of a completely new rocket created using their ideas and solutions. Already at the beginning of 1959, an order appeared for the design of such weapons. Soon the main contractor was selected - the contract for the development of the rocket was received by the aircraft manufacturer Douglas. It is curious that she had not previously participated in the WS-199 program, but her version of the new project looked the most successful.
Initially, the project was given the faceless designation WS-138A or Weapon System 138A ("138A" weapon system). Later, the army designation GAM-87 and the name Skybolt appeared. After the introduction of a new nomenclature of missile weapons, the designation AGM-48 was introduced. Also at the test stage, experimental missiles were designated as XGAM-87 or XAGM-48. The letter "X" indicated the current stage of the project.
In 1959-60 - long before the appearance of real rockets - Skybolt products became the subject of an export contract. During this period, Great Britain faced serious difficulties in the development of the Blue Streak ballistic missile. After lengthy disputes, the British military and political leadership decided to abandon such weapons. Instead of their own ballistic missiles, it was planned to strengthen the nuclear forces with American-made WS-138A products. In March 1960, the countries agreed to supply 144 missiles. The first contract for a batch of 100 items was signed two months later.
Suspension of the Skybolt rocket to the carrier. Photo Globalsecurity.org
The shape of the future WS-138A rocket was determined taking into account the developments under the WS-199 program. The most successful was considered a two-stage scheme using only solid fuel engines. It was proposed to equip the rocket with a high-power nuclear warhead, the dimensions and weight of which corresponded to its capabilities. The inertial navigation system, traditional for ballistic missiles of that time, was planned to be supplemented with astro-correction means, which made it possible to increase the accuracy of shooting.
The main element of the WS-138A rocket was a metal body built on the basis of a skeleton. The hull was equipped with a long tapered head fairing with a rounded nose. In the early stages of testing, a short cone fairing with a small diameter cylindrical wall was also used. The main body, divided into two stages, was in the form of a cylinder with several protruding longitudinal casings on the outer surface. In the tail of the rocket there were eight triangular planes. Larger swept planes served as stabilizers. Between them were placed rotary aerodynamic rudders, which were smaller. The tail section of the hull during flight on the carrier's pylon was covered by a discarded ogival fairing. The steps, the head part and the fairing were connected to each other using fire bolts.
The rocket did not have a complex layout. The volumes inside the head fairing were given for the installation of the warhead and control systems. All other compartments of both stages housed a pair of large solid-propellant engines. In the tail section of the first stage, at the level of the planes, steering gears were also located.
Prototypes on which the optimal shape of the fairing was worked out. Photo by US Air Force
The power plant for the Skybolt rocket was developed by Aerojet. For the first stage, the XM-80 engine was developed, for the second - the XM-81. Unlike previous projects, this time the engines were not borrowed from existing missiles, but were developed specifically for the new product in accordance with the requirements.
Northrop was appointed as a subcontractor responsible for the design and manufacture of guidance systems. Based on the existing developments, a new inertial navigation system was developed, integrated into the autopilot. For the first time in American practice, an astrocorrector was used to improve the accuracy of shooting. In-flight control was proposed to be carried out in different ways. The first stage was equipped with aerodynamic rudders, while the second used a movable engine nozzle that changes the thrust vector.
In the basic configuration, intended for the US Air Force, the WS-138A rocket was supposed to carry a thermonuclear warhead of the W59 type. This product had a length of 1.2 m with a maximum diameter of 415 mm and weighed about 250 kg. The power of its charge was determined at the level of 1 Mt. Specifically for the new rocket, General Electric has developed a new body with means of protecting the warhead from external influences when descending to the target.
The British military wanted to buy missiles with different combat equipment. In their case, Skybolt missiles should have been equipped with a 1,1Mt Red Snow type thermonuclear charge. This product was different from the American W59, but did not require significant rework of the delivery vehicle. At the same time, the large mass of the alternative warhead was supposed to lead to a serious reduction in the flight range. However, as the calculations showed, this made it possible to solve certain combat missions.
B-52 bomber with four GAM-87 missiles under the wing. Photo by Wikimedia Commoms
The WS-138A rocket in the transport position had a total length (including the dropping tail fairing) of just under 11.7 m. The hull diameter was 890 mm. The scope of the stabilizers is 1.68 m. The launch weight was determined at 11 thousand pounds - a little less than 5 tons. According to calculations, in flight, the rocket had to develop a high speed, which ensured flight along a ballistic trajectory over a considerable range. In its basic configuration, it could send a "light" warhead to 1,850 km. The firing range with the Red Snow warhead was reduced to 970 km. However, the British military calculated that in this case, too, the carrier bomber would be able to attack Moscow without entering Soviet airspace.
The main carrier of the promising missile was supposed to be a long-range bomber Boeing B-52G Stratofortress. The large-sized rocket could only be transported on an external sling. Up to four missiles could be placed on the pylons under the center section. The possibility of including WS-138A missiles in the armament range of the B-58 Hustler and XB-70 Valkyrie bombers was also being worked out.
In the Royal Air Force, the new missiles were to be used by V-series bombers. Already during the design, it became clear that only one of the three existing aircraft could become the carrier of the WS-138A. The rocket was placed only under the bottom of the Avro Vulcan bomber. In the case of the Vickers Valiant and Handley Page Victor machines, the "ground clearance" under the weapon turned out to be insufficient, which could lead to an accident.
View from a different angle. Photo Globalsecurity.org
Regardless of the carrier and the type of warhead, the flight program of promising missiles was supposed to look the same. The product was dropped at the carrier's cruising speed at an altitude of several kilometers. Having separated from the aircraft, it was supposed to "fall through" 120 m in height, after which the tail fairing was dropped and the first stage engine was started. Immediately after turning on the engine, the rocket had to go into a climb with a given angle. The engine ran for 100 s, after which the first stage was separated and the second stage engine was turned on.
With the help of engines of both stages, the WS-138A rocket was supposed to rise to an altitude of about 60 km. On the active section of the trajectory, the automatics determined the position of the rocket and corrected the course. After lifting the rocket to a given altitude and accelerating to a speed of about 2, 8 km / s, the second stage was turned off and dropped. Further, the flight continued only with the warhead. During firing at the maximum range, he could climb to an altitude of 480 km, after which he began to descend to his target.
Shortly after the start of project development, Douglas began full-scale aerodynamic testing. The site for them was the Eglin airbase (Florida) and the nearest training grounds. Models of WS-138A / GAM-87 missiles were taken out using standard carriers. At the same time, their interaction with the aircraft and the effect on its characteristics were determined. Also, the dummies were dumped with the collection of the necessary data. The first such test took place in January 1961, and tests continued over the next several months. These checks resulted in improvements to the existing hull and aerodynamic surfaces.
A mock Skybolt missile with British insignia at the Royal Air Force Museum (Cosford). Photo Globalsecurity.org
By the spring of next year, the project was ready to launch full-fledged flight tests. On April 19, 1962, the B-52G aircraft for the first time dropped a real XGAM-87 rocket from the pylon, on board which all standard equipment was present, with the exception of the warhead. The rocket was supposed to fly away towards the Atlantic Ocean. The first stage worked correctly, but when the second engine was ignited, a failure occurred. The rocket could not continue its flight, the testers had to use its self-liquidator.
After investigating the causes of the accident and finalizing the project, the tests continued. On June 29, the second discharge took place. This time, the prototype rocket failed to start the first stage engine. In the third start on September 13, the engine turned on, but the control systems failed. The rocket deviated from the set course, and at the 58th second of the flight it had to be detonated in order to avoid falling outside the permitted area. On September 25, the fourth rocket used the first stage and turned on the second, but its engine stopped ahead of time. The flight to the calculated range proved to be impossible. The next launch on November 28 ended in an accident again. At the 4th second of the flight, the rocket lost contact with ground means, and it had to be destroyed.
On December 22, 1962, the XGAM-87 Skybolt rocket performed its first successful flight. On the sixth attempt, the prototype was able to correctly use both engines and bring the inert warhead to the required trajectory. In the course of this check, the calculated characteristics of the range and accuracy of fire using the W59 warhead were confirmed.
However, by this time the fate of the project was decided. The military and political leadership of the United States no longer saw the point in continuing the work. At the same time, the administration of President John F. Kennedy found several reasons for abandoning the new rocket at once. Its fate could be affected by factors of a technical, economic, military and political nature.
Tail fairing view. Photo Wikimedia Commons
First, the GAM-87 rocket looked, to put it mildly, unsuccessful. Of the six test flights, only one was successfully completed. No one could say when the rockets would show the required reliability, and what the final cost of the program would be. In addition, the desired results were obtained in the field of ballistic missiles for submarines, which could take over the tasks of the Skybolt system. Finally, after the recent Cuban missile crisis, Washington wanted to show its desire for peace, and this required a demonstrative abandonment of any nuclear weapons project.
In such a situation, the WS-138A / GAM-87 project did not have a single chance. In November 1962, a decision was made in principle, and on December 22, J. F. Kennedy signed a decree to end the development of a new aeroballistic missile. Ironically, this happened on the day of the only successful test launch. However, the work was not stopped. By this time, the Douglas company and related enterprises had managed to manufacture a number of experimental missiles, and it was planned to use them in new tests to work out certain issues.
The decision of the US leadership to abandon the further development of the GAM-87 product outraged official London. In accordance with the 1960 agreement, these missiles were to enter service with the Royal Air Force and become perhaps their most powerful weapon. The refusal to develop, in turn, hit hard on the prospects of the British strategic nuclear forces. The countries were forced to start special negotiations, the purpose of which was to develop new plans for the joint development of Britain's nuclear triad.
J. F. Kennedy held talks with British Prime Minister Harold Macmillan, which resulted in the signing of the Nassau Pact. Instead of Skybolt aircraft missiles, the United States offered to supply UGM-27 Polaris products for submarines. The preliminary agreement was confirmed by the contract dated April 6, 1963. The missile shipments soon began, thanks to which the UK was able to create the desired nuclear shield.
According to known data, tests of the remaining WS-138A / XGAM-87 missiles continued throughout almost the entire 1963 year. In June, the Pentagon introduced a new range of missile weapons, according to which Skybolt was renamed AGM-48. Already under the new name, the existing missiles performed several flights. During these tests, there were both successes and accidents, but they no longer affected the outcome of the work. With their help, various issues were studied, but there was no longer a question of putting missiles into service.
The Douglas WS-138A / GAM-87 / AGM-48 / Skybolt air-launched ballistic missile could become the first model of its class to be adopted by the US Air Force. However, the presence of a mass of problems to be solved, alternative developments and the political situation in the world led to the abandonment of the project and the entire direction as a whole. The new rearmament of the strategic aviation of the US Air Force, which was launched soon, was carried out using cruise missiles.
