Beat "Brothers in Arms" on Difficult difficulty setting.

To do this easier, successfully complete the game on under the easy difficulty setting. Under the same profile, replay the intermission sequences under the normal difficulty setting, beginning with the "Brothers In Arms" scene then move to complete "Rendezvous With Destiny" to get the first two medals. Once you receive the medals for those two scenarios, quit, then play the "Victory In Carentan" intermission sequence under the normal difficulty as well. When you begin the game again, the "Infinite Ammunition" cheat will be now be accessible. The cheat must be reactivated after each chapter. Alternately, successfully complete the game under the normal difficulty setting. This cheat must be enabled again if the player is killed, retires, or starts a new level.

Beat the game on Normal difficulty setting.
Simply beat the game once on Easy. Then go to chapter select and play the very last level on a different difficulty level this will award you with that cheat.

If you are killed three times in a row, the game will offer you a chance to heal any injuries your squad might have sustained during combat. To expedite this process, you can just throw grenades at your feet.

Successfully complete the game under the difficult difficulty setting. Under the same profile, replay the intermission sequences under the authentic difficulty setting, beginning with the "Brothers In Arms" scene then move to complete "Rendezvous With Destiny" to get the first two medals. Once you receive your medals for these two scenarios, quit, then play the "Victory In Carentan" intermission sequence under the authentic difficulty setting as well. When you begin the game again, the Super Squad cheat will now be accessible. Super Squad increases the amount of hits your team (including tanks) can take before losing health, but does not affect you. If your squad begins to lose health, simply deactivate and reactivate the cheat to reset the hits and health. This works well for assaults on positions. This cheat must be reactivated after each chapter. Alternately, successfully complete the game in authentic mode.