When we were planning out all of the missions, we knew we were going to have something in a ravaged city. We were not sure if it was going to be just before it was glassed, during, or just after. Initially we wanted to do it after, and we were going to use a Scarab as the means for the player to cross the glassed terrain. So the player was going to work to hijack a Scarab and then be able to control the Scarab across parts of the edges of the glassed city.

We had a working prototype of a player-controlled Scarab and a mock-up of a section of the city. There were definite moments when you knew the context of what you were doing was going to be awesome, and some of the physics of shooting a super cannon to blow up Covenant was going to be sweet, but the act of controlling a Scarab was not something I had faith was going to be a sustainable experience for any length of time. And the cost of making the Scarab driving real was very high, so we decided to cut that mission.

But don't cry. Urk said

Every time we talk about cut content, players lament the loss, assuming the discarded scenarios and features would have made remarkable and impactful additions to the game. The reality is that these grand ideas aren't incorporated because they would be remarkable and impactful for all the wrong reasons. That's why they're ultimately cut, and that's why players won't see us resurrect "deleted scenes" as DLC.

Still, a playable scarab, oooh! Anyway, how do you persuade all those worms to go where you want them to go? Or would it have been a h2, basket-handle scarab?