Salyut 3
Salyut 3 was launched into orbit on 25 June 1974 by a Proton rocket. It stayed in space for 213 days before being burned up in the atmosphere. Starting on 4 July 1974 a crew of two cosmonauts stayed at the station for two weeks. Then on 26 August 1974 a second crew arrived but could not connect to the station and so had to return to earth.  After this no other crews visited, but the station could do some tasks on its own. One was sending the Earth-return capsule back. The second was firing the cannon. This is the only time a gun has been fired in space. A total of 20 rounds were fired in 3 bursts.