Unlock all levels:
To unlock all levels, at the chapter selection screen, while holding select press right, right, left, left, square.

Invincibilty:
To activate Invincibilty, hold L2 and press square, triangle, triangle, square. Release L2. Then, while holding R2, press triangle, square, square, triangle.

Enhance weapons:
To enhance weapons, hold L2 and press L1, L1, L1. Release L2. Then, while holding R2, press R1, R1, R1.

Veteran interviews:
To unlock interviews with veterans Gordon Boulton, Sgt. John D. "Bud" Hawk, and Sgt. Stan Markut, beat the game.

Use scope on any gun:
Your binoculars can be used as a scope by using the center of them as the sight.