During gameplay press R1, Circle, R2, L2, Square and if you entered the code correctly a message will appear. Use the Smoke grenades as diversions or to escape sticky situations by using the smoke as cover.

In the Mace mission at the stage where you have to stop the Nazis from getting to the trenches don't listen to what the men tell you, go right and follow the path and you will find a FG42 scoped beside a crate.

When you complete the game once the following interviews become unlocked.

Unlock Gordon Boulton:
Complete the game once.

Unlock Sgt. Stan Markut:
Complete the game once.

Unlock Sgt. John D. 'Bud' Hawk:
Complete the game once.

At the chapter select screen, hold down select and press Right x2, Left x2, Square x2