It is a game in wich you can't build unitis/buildings, it is more about combat than about economy,you receive some points after each mission, you can buy units/upgrades before each mission with that points(a trick it is to buy a better thank , and move the veteran crew in new one), you can go with the veteran crew from one mission to another...

From time to time you actually can find reinforcements on the maps. Not every map, mind, but every once and again. Sometimes you can rescue a tank crew and then find a tank. Other times you just find reinforcements. Although, it's been years since I played these games.