The U.S. Air Force MOL program from 1963 has been partly declassified. Space.com has a great article about the planned military space station.
NASA: MOL space suits
Popular Science: The Manned Orbital Laboratory the Air Force failed to launch
Secret Spacecraft: MOL
The U.S. wasn’t alone having secrets. It’s known that the Russian military space stations were armed but its just recently we learned the details about machine guns in space.
Popular Mechanics: Soviet Union’s secret Space Cannon
Popular Science: Soviet Space Station fired gun in orbit