Comment by leoh
Although Duga was an impressive infrastructure project, I don't really think there is anything beyond theory suggesting it could have detected ICBMs (or done much of anything else for that matter); and although the computational technology is interesting and exotic, it was almost certainly lightyears behind computers in the west. Cray-1 was already in production at Los Alamos in the 1970s.
This was a culture that said Chernobyl's reactor design was safe. Far less avarice would be required to suggest that a giant lattice of metal with exotic computers inside of it could actually do something useful.
This comment seemed overly dismissive, so I took 20 minutes to read on Over-the-Horizon Radar systems. They do work and a lot of countries have developed and operated suck systems including the USA, the UK, Canada, France and China.
The prototype Duga radar was able to detect Soviet launches from Kazakhstan and the Pacific. The Soviet Union also maintained a number of other such systems and Russia still develops and uses similar types of radars.