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Do you know if it was real-time or turn-based?
MAX is sci-fi and kind of meets what you describe, including not knowing how most of the game worked (I still don't know, myself). http://www.gog.com/game/m_a_x_m_a_x_2
If real-time, maybe the first Allies mission of Command & Conquer: Red Alert where you will get zapped by tesla coil towers if you don't knock out the base's power.
I remember when I was very small, my father had this game installed on his computer that I could never beat. I was born in the late 90s, but my dad was around to fight in Vietnam, so I have no idea when it might have been released, other than before 2004-ish. I recall it was some kind of sci-fi strategy game, I think. I only remember part of one specific level, so I don't know how most of the game worked. I remember starting with a small squad of infantry trying to sneak past a number of enemy towers. The terain was sparsely forested and heavily snowed. If anyone has any idea what game this is, I would vastly appreciate help.