Short answers, pulled from the story.
The Salyut programme began on the 15th of February 1970 after engineers at OKB-1 merged Vladimir Chelomey's Almaz-OPS hull with Sergei Korolev's civilian DOS core. This collaboration combined technologies from two fierce rivals to create a single project that launched the world's first space station.
Salyut 2 became Kosmos 557 following its launch failure on the 4th of April 1973. The station reentered Earth's atmosphere just nine hours later, marking a significant engineering setback for the early programme.
Out of 1,697 total days of occupancy across all Salyut crews, Salyut 6 and Salyut 7 accounted for 1,499 days combined. These stations became the workhorses of the entire programme through their dual-port architecture enabling continuous human occupation.
The Soviet Union utilized civilian stations as cover for the highly secretive military Almaz reconnaissance program because Vladimir Chelomey's organization designed the Almaz-OPS cores as dedicated military platforms. Two crewed military reconnaissance space stations flew under the standard Salyut designation throughout the programme while offering a cover story that finished within one year.
Small modifications had to be made to the docking port of the OPS module to accommodate Soyuz spacecraft alongside TKS spacecraft. This arrangement allowed the civilian DOS stations to offer a cover story while finishing within one year and at least a year earlier than pure Almaz designs.