well i dont have mutch info but ive bin looking for this game for some time now. played it meny meny years agoe but dont remember the name of it.
its a "space" turnbased game
you get a map like risk/showgon and its human vs alien
you can then advance in the map and so will the aliens(npc)
you build tanks and upgrade your towns. each time you advance thers new ground to be held . all mowes are done in squares
im not sure but i think the top tank was calle mamuth somthing. and its not read alert or somehting like that.
its a spacy game and would like to get my hands on it again. someone know what game that is?
Regards Tim

HI,
I browsed a little through Mobygames. Thats what I came up with:
At first I thought mhmm Battle Island 1 or 2
http://tinyurl.com/battleIsle
http://tinyurl.com/BattleIsle2
But there are no aliens and as far as space goes: only one Mission Disk played on the moon.
However there was a Mammoth style tank in BI2 I think.
On the other hand there is Star General, a Panzer General in space.
http://tinyurl.com/StarGeneral
But i never played it, so i dont know how far it matches with your memories.
I sugest you have a look in the mobygames browser, here with categories scifi-strategy-dos-topdown selected
http://tinyurl.com/MobyBrowserSfTdStrDos

Can't really think of any game that comes close to what you described, but maybe the following might jog your memory?
Alpha Centauri
Deadlock
Master of Orion