Avoid air attack
When your opponent sends an air attack, display the menu and wait the sound of the bullets. Wait 25 to 30 seconds afterwards and resume. The attack will not appear and your soldiers will not be dead.
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.
Getting more upgrades
When your "Upgrade" button has any number during a battle, select it. Use it on a upgrade. When you complete the mission, look at the "Upgrade" icon. You will still have the same amount of upgrade points that you already used.
Immediately click "Custom Game" then launch the mission. Note: Do not adjust a custom battle. As soon as the custom battle begins, quickly exit to main menu. At main menu, start an allied campaign and the mission will be "undefined".