Arma 3 is one possible implementation of this. BUT, it requires to download and install mods, find (a lot) of people to play with. The way it's made requires a

Arma 3 is one possible implementation of this. BUT, it requires to download and install mods, find (a lot) of people to play with. The way it's made requires a lot of dedication -> gathering everyone, organisation to communicate can be tricky particularly if you want realistic kind of comms: teamspeak is still required (I don't think there's a realistic mod for Arma 3 compatible with Discord). Nevertheless, Arma 3 has everything you need: Big maps (open world) An actual map (I am talking about the paper/GPS thing) -> with actual elevation information on it, etc. Complex strategies and tactics possibilities Communications Vehicles: helicopters, tanks, cars, trucks, planes, boats, etc. etc. A very WIDE set of weapons of all kinds: turrets, firearms, launchers, mortars, etc. etc. All this adds up to the need of coordination, planning, preparing strategies, primary objectives, secondary objectives, backup plans, backup plans for your backup plans, etc.