The Tank Factory is the only building in Empire Earth that produces tanks. Like many other factories, the Tank Factory takes time to train units and it lets you place a rally point. The Tank Factory is first available in the WW1 epoch, epoch 10. The useful thing about a tank factory is that they produce ground to air guns as well as ground to ground guns, so in other words they produce portable Anti Aircraft and portable tanks that shoot other tanks. Eventually, when you are allowed the missile base (in epoch 13), you will get a Anti Missile Battery to stop nuclear missiles.