Well, it's not a 100% tank sim... More like a nice side-feature to a WWI flight sim mod; a mod to a mod so-to-speak.

You can man the gunner positions (Machine guns and the cannon). Currently, the AI really isn't set up well for ground warfare, so we use static tank units in key tactical positions. So, when you take over a gunner position the AI just keeps driving the tank slowly forward. I'm working on making the AI more adapt to driving on the ground however. There are single player campaigns (One per tank) in which you are the "lone wolf" that drives and shoots and the rest of the units are static. You of course have static units on your side that provide covering fire and support.
Currently, the list of drivable tanks are the German A7V, British Mk.IV, French FT-17 and French St. Chamond. These were built long ago, around 2003 so the 3d modeling and texturing isn't up to today's standards. But, it's fun none-the-less! And makes great on-line play.
All of this is in the FS-WWI Plane Pack 5 offering, a free WWI flightsim mod where you don't need any original game CD to play. Gotten here:
http://www.moddb.com/mods/fighter-squadr...e-exe-installerI will post more pics soon.