In 1958, I supervised a series of studies to see how the size and shape of objects, and the length of radar waves, interacted to produce radar signatures. I had to design a new test chamber with a low radar signature so that we would to be able to perform these measurements. One of the object shapes I tested was an elongated triangle, like a Toblerone chocolate candy box, or the triangular boxes that some posters are shipped in. You can see what I call the ‘triangular cylinder’ end-on in the center of the patch; it is the gray triangle.
We bounced radar waves of various wavelengths off of the long sides of the cylinder as the cylinder was rotated. When the radar wavelength was only about 1/25th the length of the triangle’s side, we produced the radar signature shown in red on the patch. The radar signature was very low most of the time, spiking to a maximum when broadside to the triangular cylinder faces, and falling quickly to the lows as the cylinder turned. Longer radar wavelengths produced wider broadside spikes and higher off-normal returns, resulting in higher radar cross sections.
Using the very data represented on the patch, I told Kelly Johnson in 1959 during the Arrow series design process leading to the A-12 Oxcart, and Dick Scherrer in 1974 during the conceptual design of Have Blue, predecessor of the F-117 Nighthawk, that the secret to low radar signature aircraft was to shape them to have nearly flat surfaces that would be as much as twenty-five times larger than the enemy radar’s wavelength. This design guideline also was incorporated into Lockheed’s stealthy ship, the Sea Shadow, which was launched into radar signature testing at sea in 1985