Kill at least one enemy with every weapon in the game. (Single Player)

These carry through each playthrough. All weapons are dropped by enemies frequently.

Mission - SNAFU
Sap9- Starting weapon
Sm5 - starting weapon
Knife (kill move)
Grenade
Ak74
OTS-02
Pecheneg
Type 97-1
Dragunov (you will come to a building where you fast rope down for the first time, before you do there is a Dragunov laying on the table to the right.
Mission 3 - GNBN
Spas 12 (you will come to an area with this lying on a shelf, its impossible to miss)
Ar 4 (in the harbor area, at the beginning make your way to the left and you will see a group of enemies burst out of a building, kill them then enter the building to find this lying on a gun shelf)
GM-94 (Its located in the harbor area when you first get attacked by people on the ship, its to the right as you walk around the corner to said ship, lying on an ammo box)
Mission 5 - FUBAR
TT-33 ( after passing over the bridge you will enter a small building to continue, it is lying next to the exit on some ammo boxes. Again, impossible to miss.
Note the majority of these weapons can be located throughout the game, this is just the first place you will find each weapon.