To complete this easily, put in this code: L1, R1, triangle, L1, R1, O, L1, R1, it's the $250,000 cheat. Then, go to ammu-nation and get the micro SMG. Keep buying ammo for it until you can't buy any more, then head for vincenzos place (at portland docks), and start the mission. Go down to the freighter, as prompted, and then into the hull, then shoot 3 of the closest ones, then run around, with EVERY SINGLE ONE behind you, after a while, you speed up, shoot one, then run, and repeat the process. Once all of them are gone, Vincenzo comes in with an AK/M4. Kill him, it's easy, and run out. You get $3000 for completing this mission.