That time the US collected Soviet radar technology via the moon
A U-2 spyplane captured a strange photo in 1960; the Soviets had built a massive new antenna near a missile test range. The CIA and others immediately suspected that the array was part of a new radar system and wanted to figure out what its capabilities were, but it was deep in defended space.
So American intelligence decided to try a newly discovered option. In 1946, the U.S. Army Signal Corps had bounced communications signals off of the moon, proving that it had a suitable surface for relaying signals. The Navy spent the next decade building a system that would allow communications between far flung ships and bases by reflecting the signals off the moon.
So the CIA, after they ruled out further collection by aircraft, decided for a literal moonshot. They would train highly sensitive antennas on the moon and wait for the Soviets to scan an object in front of the moon. When the radar energy that passed the target struck the moon and bounced back to the earth, the CIA could collect information from it to figure out how the new radar worked.
But the effort required truly massive receiving antennas. Most of the available antennas that would suffice were 150 feet wide and the best was a proposed 600-foot dish that was never completed. Even then, the CIA needed to get lucky and be looking at the same moment that the Soviet Union was using the radar in the direction of the moon.
They would get insanely lucky.
The first break came in 1962 when the Soviet Union inadvertently reflected radar data out, not from the moon, but from their own atomic testing. The nuclear detonation created an ionized cloud that reflected signals and allowed some limited intercept.
In 1964, the CIA was able to start regularly collecting data from the Soviet site, dubbed the "Hen House Site," after it reflected off the moon. A specially modified receiving station in Palo Alto, California, picked up the signals.
To the surprise and delight of the CIA, the Russians began tracking the moon with the radar for practice, giving the U.S. up to 30 minutes at a time of continuous data. A CIA historical document detailing the effort said:
We expected to see a regular scanning, or "search" mode, and a tracking mode, where the beam follows a target. Both of these have been observed. In the latter, the Soviets, apparently just for practice, have set the radar to track the moon for as much as half an hour. This makes the intercept job much easier, as we then see the signal continuously rather than in short bursts as the beam swings by the moon.
The radar system was estimated to be quite sophisticated, capable of not only identifying and tracking individual targets but of tracking multiple targets and quickly switching focus between them. The system was so fast that the CIA felt confident it was controlled by a computer.
All in all, it made the system a serious threat to American efforts. It would later come to light that the system was designed to track and potentially defeat ballistic missiles. If successful, it could have negated the American nuclear deterrent.
Thanks to the efforts of the CIA, though, America was able to get a jump on the Russians and steal back the advantage.