Almaz

Almaz was a space program by the military of the Soviet Union. Its purpose was to spy on other countries using space stations. After some time, the program changed to using spy satellites instead.
Since it is hard to hide a space station, the Soviets tried to keep the program a secret another way. They pretended the stations were civilian and gave them names in the Salyut series. The Salyut stations (such as Salyut 1) were normally to learn about how to live in space.
The Almaz program sent three stations to space, but the first failed. In the later years of the program, satellites were used instead since they are cheaper.
Space stations.
The Almaz program sent three space stations to space. These were Salyut 2, Salyut 3, and Salyut 5. These had large space telescopes to spy on other countries. The cosmonauts on the station operated these and used cameras to record what they saw.
The Salyut 3 station also had a large cannon, which was test fired once.
Satellites.
In 1978, Almaz began to using spy satellites instead of space stations. Four were made as part of the program. These used radar to observe the ground instead of telescopes.
The first was Almaz-T which launched on 29 October 1986. The Proton rocket in launched on failed, and was destroyed by its safety system. The next was Almaz-T2, which went to space on 25 July 1987 and stayed in space for two years. The third was Almaz-1 which launched on 3 March 1991 and stayed in space for 18 months. A fourth satellite (Almaz-2) was built but never sent to space.
Legacy.
The design of the Almaz space stations continues to be used even today. The Zarya module of the International Space Station is based on it. And before that, the Kvant-1 module of Mir was based on it.