Ultravanillasmurf, I think the rule set you are trying to recall was called “Operational Manoeuvre Group”. I may still have them somewhere but never played them.
Here they are in their red brown glory with cover art to warm Carlos' heart

I do recall Challenger. From memory managed 2 turns in about 3 hours of gaming!
Wow! Speedy.
I remember playing Challenger (I or II - I cannot remember) on gaming weekends.
I would set up the board (a 6'x4' piece of chipboard, with paperback books to build the hills then covered with a felt sheet and the contents of a bumper bag of lichen from Beatties) first thing Saturday morning. We would start about 1000 and play on to 2000+.
The first round after Contact would take about two plus hours. This would reduce drastically as units were destroyed.
We did play the first contact scenario from the GDW Team Yankee game using Challenger one weekend.
A following session we continued the campaign, with the surviving forces entering the second line defence line. First on to the table was one T72 that had made it through Team Yankee's defence line - hotly pursued by the surviving US forces, then the second Soviet wave.