Dynamic Campaign Generator (DCG) is a mod for the game "Men of War" and some of its successors that randomly generates skirmish missions and lets you keep your surviving forces from one battle to another. Some people find this mod tricky to install the first time - please read the readme.txt carefully and ask for help (if you need it) on our forums here on this site, or at the game developer's site.
The concept is nothing short of inspired. The execution is nothing short of elitist. A good thing? If you're really into facing Starship Troopers amounts of enemies then yes. If you are looking to be challenged this is different, 'if' you survive the first mission your remaining soldiers will tell a story that sound suspiciously the Battle of Thermopylae, (that would be the 7,000 Spartans holding off the horde of Persia.)
You will run out of ammo. You will run out of Fuel. You will run out of repair kits. You will fight them in the fields.. and in the streets. You will probably surrender in angst at the second mission as you lost your cheapy tank and the opponent brings in 15 of his best ones from magic.
But I must say this: If you are successful enough, you can reach the level where it is fair. This is when it becomes fun. Hang in there for that but beware: the second campaign will see the sky run dark with the bullets and your computer will almost with certainty lock up as your minimap turns red.