Obviously, it wouldn't be a scuba fight without some breathing apparatus. My initial concept is for an initial skirmish outside the facility, a breaching scene as the attackers force an entry, and then some tunnel fighting down those passage ways and a last-stand.
The orange diver looks a lot more high-tech than the black-suited one: That's because she'll be with the outnumbered defenders, and the lower-tech attackers will be using weight of numbers to overwhelm their opponents.