www.matrixgames.com
Armored Brigade, through GoG. Excellent cold-war era military pseudo-RTS (pause-button available).
Incredible line-of-sight / fog of war simulator. Dwarf-fortress level detail for combat. (Virtually every bullet is tracked: angle of striking a tank, probability of deflection, distance, penetration of armor, chemical-energy vs kinetic energy, tandem, top-attack, guided, fire-and-forget simulated effects).
Land / Air combat only. Air combat is very primitive (call for air support from a certain direction and heading. Its "simulating" as if a different Commander controls the Air Support call). Artillery support is much better and faster.
Typical commands take 1.5 minutes to execute (!!!!), and some calls can take 8 to 20 minutes (!!!) realtime. For any RTS player, you'll find it to be a challenge to coordinate your troops, since APM literally doesn't matter anymore. The long time it takes for commands to be "received" leads to a very strategic feel. You end up chaining a long set of commands all at once(fast-move here then advance slowly to here, stop and unload on contact, pop smoke, 300m soft engagement, 800m hard engagement, defend from this direction).
Single Player only, unfortunately. Computer AI is kinda dumb and easy to trick, but is more than adequate enough to challenge you (especially with superior numbers in most cases). Difficulty of this game is quite high, be ready to lose a lot of times in combat to learn how things work.