Hold Plus and press Right two times, Left two times, 2 two times at the chapter selection screen.

On the second mission, "The Island", there will be a man under the second bridge with a FG42 scoped. That gun will get more ammunition every time you kill someone. The gun starts with 96 ammo remaining and you can kill about 150 people with it (not including melee). After completing that mission you will have that gun on the third mission, but you must save the gun through the third mission to get it in the fourth mission and so on.

When you meet up with the French rebels you will have a choice to go left to the Flak 88s or go through the house to the right. Go left to the guns. Kill all the Nazis around the gun and in the ditch leading to the next gun. Then, blow up the 88 and move on to the rest of the guns. After you blow up all the guns you will reach the house that you would have had to take if you went right. When you go in the house you must defeat a Nazi that is standing there waiting for you. Kill all the enemies in the house and fall through the burning floor. You will see you allies there waiting for you.

Normally, you're only supposed to hold 6 grenades but when you have a grenade thrown at you you can pick it up and throw it again. Instead of throwing it you can keep it for later by pressing the minus button a second time after picking up a grenade. There's no limitation of grenades when doing this.

When a grenade is thrown at u stand right next to it and hold - quickly aim and press <- it will throw the grenade but be quick or else it'll blow up on you but might not kill you.