Both the United States and The Soviet Union signed the treaty, but it's hard for weapons inspectors to go to space to confirm. Rumored for decades, a 1970s Soviet space cannon was earlier this year finally revealed on Russian television.

Originally built for Russia's Tu-22 Blinder supersonic bomber, the R-23 gun was mounted in the plane's tail as a deadly surprise for any pursuing jet fighters. The gas-powered gun could fire 23mm rounds incredibly quickly. It's a variant of this gun that made it to space, on board one of the Soviet Union'sAlmaz military reconnaissance space stations.