SM-64 Navaho
The North American SM-64 Navaho was a supersonic intercontinental cruise missile project built by North American Aviation. The final design was capable of delivering a nuclear weapon to the USSR from bases within the US, while cruising at at altitude. The missile was named after the Navajo Nation, starting with "NA" for North American, it is sometimes stated to also be an acronym for North American Vehicle, Alcohol, Hydrogen peroxide, Oxygen, referring to the missile's propellants.
The original 1946 project called for a relatively short-range system, a boost-glide weapon based on a winged V-2 rocket design. Over time the requirements were repeatedly extended, both due to the US Air Force's desire for longer ranged systems, as well as competition from similar weapons that successfully filled the shorter-range niche. This led to a new design based on a ramjet powered cruise missile, which also developed into a series of ever-larger versions, along with the booster rockets to launch them up to speed.
Through this period the US Air Force was developing the SM-65 Atlas, based on rocket technology developed for Navaho. Atlas filled the same performance goals but could do so with total flight times measured in minutes rather than hours, and flying at speeds and altitudes which made them immune to interception, as opposed to merely very difficult to intercept as in the case of Navaho. With the launch of Sputnik 1 in 1957 and the ensuing fears of a missile gap, Atlas received the highest development authority. Navaho continued as a backup, before being canceled in 1958 when Atlas successfully matured.
Although Navaho did not enter service, its development provided useful research in a number of fields. A version of the Navaho airframe powered by a single turbojet became the AGM-28 Hound Dog, which was carried towards its targets on the Boeing B-52 Stratofortress and then flew the rest of the way at about Mach 2. The guidance system was used to guide the first Polaris submarines. The booster engine design, spun off to NAA's new Rocketdyne subsidiary, was used in various versions of the Atlas, PGM-11 Redstone, PGM-17 Thor, PGM-19 Jupiter, Mercury-Redstone, and the Juno series; it is therefore the direct ancestor of the engines used to launch the Saturn I and Saturn V Moon rockets.
Development
Postwar Army missile studies
The Germans had introduced a number of new "wonder weapons" during the war that were of great interest to all the allied forces. Jet engines were already widely used after their introduction in the UK, but the V-1 flying bomb and V-2 rocket represented technologies that had not been developed elsewhere. In German use these weapons had relatively little strategic effect and had to be fired in the thousands to cause any real damage. But if armed with a nuclear weapon, even a single such weapon would cause damage equivalent to thousands of conventionally armed versions, and this line of research was quickly taken up by the US Army Air Force in late 1944.Vannevar Bush of the USAAF's Scientific Advisory Board was convinced that manned or automated aircraft like the V-1 were the only possible solution for long range roles. A ballistic missile capable of carrying even the smallest warhead was "at least ten years away", and when asked directly about the topic, noted:
Army planners began planning for a wide variety of post-war missile systems that varied from short-range ballistic missiles to long range flying bombs. After considerable internal debate among Army branches, in August 1945 these were codified in a classified document outlining many such systems, among them a variety of cruise missiles, essentially V-1s with extended range and the greater payload needed to carry a nuclear warhead. There were three broad outlines depending on range, one for a missile flying, another, and finally one for. Both subsonic and supersonic designs would be considered.
Competing designs
The various proposals were sent to seventeen aviation firms on 31 October 1945. Of the many proposals received, six companies were granted development contracts. Submissions for the longer-range requirements were all based on cruise missile designs, while the shorter-range examples were a mixture of designs. These were assigned designations in keeping with the USAAF's Experimental Engineering Section's "MX" series.NAA chief designer, Dutch Kindelberger, was convinced missiles were the future, and hired William Bollay from the US Navy's Bureau of Aeronautics to run their newly formed research laboratory. Bollay had previously run the Navy's turbojet development. Bollay arrived to find the Army proposals, and decided to submit a short-range design based on a winged ballistic missile based on the German A-4b design, a development of the basic V-2. On 24 March 1946, NAA received letter contract W33-038-ac-1491 for this missile, designated MX-770. The initial design called for a range of with a payload, but on 26 July this was increased to.
A number of other designs were also accepted, but these were all cruise missile designs to fill the longer range requirements. These were Martin's MX-771-A for a subsonic missile and -B for a supersonic version, MX-772-A and -B from Curtiss-Wright, MX-773-A and -B from Republic Aircraft, and MX-775-A and -B from Northrop. It was intended that one subsonic and one supersonic design would be put into production, and these were granted the designations SSM-A-1 and SSM-A-2, respectively. The only ballistic missile in the group, MX-774, went to Consolidated-Vultee.
When President Harry S. Truman ordered a massive cut in military spending for FY1947, as part of the Truman Doctrine, the USAAF was forced to make major cuts to their missile development program. Missile funding was cut from $29million to $13million. In what became known as "the black Christmas of 1946", many of the original projects were cancelled, with the remaining companies working on a single design instead of two. Only Martin continued development of a subsonic design, their MX-771-A, delivering the first SSM-A-1 Matador in 1949. The rest of the companies were told to work only on supersonic designs.
Engine work
NAA began experimenting with rocket engines in 1946, firing the rockets in the company parking lot and protecting the cars by parking a bulldozer in front of the engines. They first used a design from Aerojet, and then designed their own model of. By the spring of 1946, captured German data was being disseminated around the industry. In June 1946 the team decided to abandon their own designs and build a new engine based on the V-2's Model 39.In late 1946, two Model 39 engines were sent to NAA for study, where they were referred to as the XLR-41 Mark I. "XLR" referred to "eXperimental Liquid Rocket", a new designation system being used by the Army Air Force. They used these as the basis for conversion from metric to SAE measurements and US construction techniques, which they called the Mark II.
During this period, the company received a number of late-war reports on developments of a Model 39a engine for the V-2, which replaced the original model's eighteen separate combustion chambers with a single "shower head" plate inside a single larger chamber. This not only simplified the design, it also made it lighter and improved performance. The Germans were never able to get this working due to combustion instability and continued using the earlier design in spite of lower performance.
The team that had designed the engine was now in the United States after being captured as part of Operation Paperclip. Many of them were setting up a new Army-funded research effort under the direction of Wernher von Braun. The company hired Dieter Huzel to act as a coordinator between NAA and the Army missile team. In September 1947, the company began the design of an engine incorporating the showerhead design, which they called the Mark III. Initially, the goal was to match the thrust of the Model 39, but be 15% lighter.
Work on the Mark II continued and the detailed design was completed in June 1947. In March, the company rented a large tract of land in the western San Fernando Valley north of Los Angeles, in the Santa Susana Mountains, for use in testing large engines. A rocket test center was built, using $1 million of corporate funds and $1.5 million from the USAAF. The first parts began to arrive in September. Development of the Mark III proceeded in parallel using a scaled-down version developing that could be fired in the parking lot. The team made a string of changes to this and eventually cured the combustion problems.
Evolving design
Another set of German research papers received by NAA concerned work on supersonic ramjets, which appeared to make a highly supersonic cruise missile design possible. Bollay began a series of parallel design projects; Phase 1 was the original boost-glide design, Phase 2 was a design that used ramjets, and Phase 3 was a study for what sort of booster rocket would be needed to get the Phase 2 vehicle up to speed from a vertical launch system.Meanwhile, aerodynamicists in the company discovered that the A-4b's swept wing design was inherently unstable at transonic speeds. They redesigned the missile with a delta wing at the extreme rear, and canards at the nose. Engineers working on the inertial navigation system invented an entirely new design known as the Kinetic Double-Integrating Accelerometer that measured not only velocity as in the V-2's version, but then integrated that to provide the location as well. This meant that the autopilot simply had to compare the target location with the current location from the INS to develop a correction, if any, that needed to bring the missile back on target.
So, by June 1947, the original A-4b design had been changed at every point; the engine, airframe and navigation systems were now all new.