Found by yogo9
Go to the Stage Covenant and play “Ralley Point Bravo.” Get in a Vehicle and Go to the bit where You First see a Ghost. Get in the Ghost and go to the Mountain Top where you see the Hidden Marines. Drive Straight with the turbo on; You will see the Game Freeze. When it does this You will Lose the Ghost and Walk to the closest Tower (but stick to the barriers). You will see a Black Ground; Jump on it and the game will freeze and it will Teleport you to the bit where You go up the moutain to the Hidden Marines. Keep walking to where you are meant to get in the Hornets and You will come across 3 Floating brutes. Then when you get to the hornet spot there will be no hornets, only the drivers, but too bad they’re dead. Just go down the Little Hill and when You look in the air you will see the brutes fall from the sky.