Isotope He-3 is a very rare and interesting substance. For example, it becomes a fermionic superfluid when cooled below a few milliKelvin. Along with its slightly heavier brother He-4, it is one of the two quantum liquids, meaning it remains liquid (in theory) down to absolute zero temperature. By circulating it in a closed loop one can produce cryogenic temperatures below 1 degree Kelvin, where all other substances turn solid. So most low temperature experiments rely on He-3.
Here are two stories about He-3, one of them mostly true, the other mostly false. I will not tell you which is which. But I will tell you that one of them is a plot of a recent movie.
Story #1. United States government stockpiled all He-3 available on the planet. After the generals find out that He-3 can be used to detect radioactive isotopes, a plan emerges to build a wall around the U.S. borders with designated gates equipped with neutron detectors that run on He-3. As a first stage of the program, all He-3 is made unavailable and declared a national security resource. Research in low tempearture physics, medical imaging and fusion comes to the brink of a halt. A black market emerges with overpriced He-3 from shady sources like Russia and possibly Canada. Students who loose He-3 in their labs are never seen again.
Story #2. In 1945 Nazis manage to send a space ship to the dark side of the Moon. The primary mission was to harvest He-3, abundant on the Moon, which they were going to use for world domination. They have established a base and built a refinery. They also built a space fleet capable of destroying Earth. Now all they need to launch an invasion is an iPad to navigate the ship.