Before you enter the room where the boss fight happens make sure you pick up the Uzi before you enter. Shotgun and pistol works but it's a lot harder.
Make sure you have the Enforcer at the end to make the battle a bit easier.
Like Bossu before you enter the fight turn left and go behind the shed. Some useful items including a Uzi. It will take the gunship down quickly.
Press: Up, Dowm, Up, Down, Up, Down and press Start.
At the press start button screen hit circle, up, square, triangle, right and down. If you go into the Police HQ and go to cheats, all the cheats are unlocked and you can use them for Quick game only.
For unlimited ammo, enter square, triangle, down, down, up, up, left, square, circle, down.