After his tremendous successes with Vostok and Voskhod, Chief Designer Sergei Korolyev turned his sights on the development of a ship capable of reaching the moon: Soyuz. He clearly understood that in order to secure funding he would need the support of the military and thus sketched out numerous ideas for military applications of Soyuz.
In 1964 Korolyev's design nemesis Chelomei proposed the construction of an enormous military space station called Almaz (which ultimately became the basis of Mir). The Korolyev team took a more moderate approach and - being fully aware of the development of the US's military MOL - proposed a much smaller Zvezda (star) station based on a radically modified Soyuz.
The proposal was accepted in 1965 and work commenced on Zvezda anticipating a flight in 1967. Zvezda would have been powered while in orbit by 2 plutonium radioisotope generators and had a rapid-fire gun for defense against killer-satellites. A advanced design called for a forward docking apparatus to allow docking with Almaz (shown above).
Work on Zvezda was cancelled in 1967 with a single prototype in advanced stages of construction.