Cold war history

The Soviets fired this secret heavy cannon while in orbit

Most important to the USSR was the idea of American spacecraft being able to literally get their hands on Soviet satellites. Anti-satellite operations were something both powers prepared for, but the idea that the satellite itself would need protection up there all alone prompted the Soviets to arm one of theirs, just to see how that would go.

The Soviets built a station code-named "Almaz," a space station that held spy equipment, radar, and the R-23M, a 37-pound 14.5mm automatic cannon that could fire up to 5,000 rounds per minute that was accurate up to a mile away. There was just one problem: aiming the cannon. The cosmonauts in the station would have to rotate the entire space station to point the weapon.

It was supposed to be the first manned space station in orbit, but the Russians were more concerned with developing the weapon than they were other aspects of the capsule, like sensors and life support. So instead of building their grand space station, they slapped together what they had with the R-23M and a Soyuz capsule, called it the Salyut before launching it into space in 1971.