by Richard Sheffield
Since radar technology was developed during the Second World War, it should not be surprising to learn that the first attempts at stealth technology occurred during this period also. It might be surprising to learn, however, that it was the Germans, not the Allies, who worked on the project. The Germans were responding to the success the Allies were having with the early radar sets. Not only was their radar very effective at spotting incoming enemy bombers, but it was also very important in the battle for the Atlantic.
German U-Boat submarines were doing a very good job of disrupting the convoys carrying valuable supplies to England. The favorite tactic was to attack on the surface at night, often in large groups called wolf-packs. When radar appeared, this advantage was lost. In response, the Germans developed a radar absorbing paint. While this ferrite-based paint was much too heavy for aircraft, it could be used on submarines.
The United States' first stealth development was totally accidental and quickly forgotten. Shortly after the war, Northrop Aircraft developed an experimental bomber called the YB-49 Flying Wing. As the name implies, the aircraft had no body or tail; it was simply a large flying wing. The aircraft was assigned to perform a normal test flight over the Pacific. When the test was completed, they turned and headed for home, pointing the slim wing edge directly at the base radar station. The radar crew was shocked to see the aircraft suddenly appear almost overhead because they had seen no evidence of it on the radar screen. Interest in the project quickly faded after the bomber crashed in the Mojave Desert in 1948. The plane was very unstable in flight and this stability problem was listed as the cause of the crash. Ironically, the new top-secret B-2 Stealth Bomber bares a striking resemblance to this aircraft designed and built in the 1940s.
As radar equipment became more powerful and compact, the concept was all but forgotten. Emphasis was placed on developing faster aircraft, the theory being that the faster the aircraft was, the less time the radar operator would have to react to the threat. The problem with this line of thought was that as aircraft speeds increased, so did the size of the aircraft. The larger aircraft could be detected at greater distances, thus negating much of the speed advantage.
As bombers grew to the size of the B-52, it became apparent that something had to be done to reduce the effectiveness of enemy radar. Electronic jamming devices were developed to flood radar screens with returns, making it impossible to detect the source. The Quail pilotless decoy drone was also added to the B-52. This aircraft was designed to return a radar image as large as the B-52 bomber that carried it. This development is important in the history of stealth technology as it shows for the first time that the radar return of an aircraft does not depend on its size alone. The idea did not catch on right away, though, as the researchers concentrated on the development of more powerful jammers.
With the “cold war” and the Soviet Union well under way in the early 1950s, it became imperative that the U.S. should learn about military developments deep inside the country. Old bombers were converted to spy planes, but they soon proved to be very vulnerable to attack. In order to plug this intelligence gap, a new plane was designed. The idea was to create a plane that could cruise safely at very high altitudes, well out of the reach of any existing fighter. The design specification required that “consideration be given…to minimize the detectability by enemy radar.”
The task of making this plane a reality fell upon the Advanced Development Projects team at Lockheed in California. This was a small team of highly qualified and highly motivated engineers and pilots. This highly secret facility became known as the “Skunk Works” and has been on the leading edge of stealth technology since the early 1950s.
The aircraft they developed became known as the U-2, and it was highly successful. The U-2 was the first aircraft to use radarabsorbing paint known as “Iron Ball.” The aircraft was successful at penetrating Soviet airspace unobserved for a period, but it was known that eventually stronger radars and surface-to-air missiles would be developed. Of course, these systems were developed, leading to the shooting down of a U-2 and pilot Gary Powers.
U-2 aircraft in flight over the Caribbean Sea.
Project Senior Crown
By this time, however, another aircraft was already being developed. It was to be capable of even higher altitudes and incredible speeds. Not only would it be able to fly higher than any enemy fighter, it would be able to outrun enemy surface-to-air missiles. It was soon realized an aircraft with these capabilities would have to be much larger than the U-2, which was basically a powered glider. This being the case, they would have to pay much more attention to reducing the RCS, or this larger target would be spotted as easily as the U-2. A low RCS was imperative; without it the extra performance would be meaningless. If the enemy could track the aircraft, they would simply cover all sensitive material in the area and the intelligence gathered would be of no use.
The design of the A-12 aircraft (later to be the SR-71) was based on low observability. Since no other aircraft had ever been developed with this in mind, it's not surprising the resulting aircraft looked unlike anything that had ever flown.
High-angle right-side view of a Strategic Air Command SR-71 aircraft, which can cruise at a speed in excess of 2,000 mph and an altitude above 80,000 feet.
The plane was long but slim. The engines were set into the wings, not under them, and the dual tail fins were slanted inward. All these items combined to form a very sleek aircraft with a trim profile.
There were other design items that weren't so easy to spot that also had a big impact on low observability. For the first time, radar absorbing materials other than paint were used. These materials covered the wing leading edges to reduce the glinting effect of curved surfaces. Flat areas such as control surfaces were also covered with the material to reduce reflections.
Despite all the high-tech advances made by project Senior Crown, political fallout from the Gary Powers incident was heavy. Before long, there were no more manned overflights of the Soviet Union. With the very mission it had been designed for now off limits, the ADP at Lockheed set about using the A-12 technology to design a pilotless vehicle. Project Senior Bowl produced the D-21 drone. It was designed to be dropped from another aircraft, probably an A-12 or B-52. It resembles one engine and the outer wing of the A-12. More extensive use of RAM and other stealth methods made this drone almost undetectable. The D-21 would be flown by radio into enemy territory to collect data. Once clear of the enemy border, it would drop the info by parachute. This chute would be snagged by another aircraft before it hit the ground. The drone would then self-destruct over the ocean, if possible. Little is known about the program except that few were used operationally and the aircraft was retired in 1972.
Stealth in Vietnam
The war in Vietnam posed a whole new set of problems to military planners. This was not a mechanized army we were up against but one that moved primarily at night, on foot and on bicycles—a very quiet army. Without the background noise of trucks and tanks, a recon plane overhead could easily be heard. Again Lockheed was contracted to produce an aircraft capable of performing reconnaissance undetected. At first, gliders were modified. Highly muffled engines and large, slow-turning props were added with great success.
This led to the development of the Q-Star and the YO-3. These aircraft were not very fast, had no armor, and were not very maneuverable. They were the first true stealth aircraft, as they relied totally on their ability to pass undetected behind enemy lines.
Many of these earlier developments would play an important role when it came time to develop the Stealth Fighter.