Eighth Card (Cancelled late 1960s)
Reportedly named for a reference to a card game trick that would give the United States the upper hand over the Soviet Union, this once top-secret laser programme was based on a gas-dynamic carbon dioxide laser that was supposed to reach 500 kilowatts. Numerous reviews eventually determined that, among other problems, scaling it up in power while maintaining the beam quality would be impractical.
Project Seesaw (Cancelled late 1960s)
In the 1960s, the U.S. government funded the top-secret project, which looked at the feasibility of particle beams for missile defense. Bounced between various agencies, including the Advanced Research Projects Agency (now known as Darpa), the project literally see-sawed between evaluations that deemed it theoretically feasible, or practically impossible. Eventually the latter evaluation won out, and no particle beam was developed.
Project Argus (Cancelled approximately 1959)
In 1958, the United States carried out a series of top-secret nuclear tests meant to test a missile defense theory forwarded by an eccentric physicist at the Lawrence Livermore National Laboratory in California. The concept was that nuclear weapons detonated in the upper atmosphere would create an artificial radiation belt capable of stopping incoming intercontinental ballistic missiles—a sort of atmospheric missile shield. Though the tests were hailed as successful the scheme, at the time dubbed “the greatest scientific experiment ever conducted”, was deemed impractical, if not impossible, for stopping nuclear attacks, and never went beyond testing.