How do you get the scarab gun in halo2

There are 2 Methods. Method #1: Get a banshee to follow you, and right before the loading text appears hijack it. Then, fly around until you see twin towers with a bridge in between them. In the middle of a bridge should be a cone with a plasma rifle on it, that is the scarab gun. Method #2: When the scarab fight by the water comes, jump into the water in a scarab beam, and if you keep on pressing RB, if you pass the scarab gun you will switch to it. But you only have 5 seconds to use it before you fall in the water and die unless you modded it, so the first method is easier.