Fill your entire bunker with riflemen. After the enemy reaches your trench, all your riflemen will fire at the same time. Note: This only works for trenches.

Go to the main menu then to "Custom Battle". Click on "Riflemen", "Assault Team", "Machine Gun Team", then "Bazooka" and "Mortar". Set the resource points to "2000". Launch the battle on a no cover battlefield. Send all of your men in the middle. Occasionally send in reinforcements and you will have an unbeatable army.

As the U.S. on an open map, send a tank first on the side. Then, send riflemen through the middle zone. The enemy will focus on the tank, your riflemen will reach the end of the middle zone, and you will win the battle.