Make them Sandtroopers first of all. And then, you can have their ship crash before they even get to the base. Make a few get killed off by a hit and run guerilla Rebel force. Have Doman be in charge of new, freshly recruited soldiers who can work their E-11 and kill the target but can't seem to work together just yet. Doman should also be fresh from the Imp Academy so he too is a bit unexperienced in the field.
They're teamwork can unify them or something but it won't be easy. There is one guy in the group who is a real hard ass and hates Doman. He thinks he's unexperienced and that he should be leader instead. They settle their differences after Doman saves his life or something. They eventually get the the base and begin a raid. They get through a sector of security before they reach the first sealed blast door. They call up for their engineer and await his arrival. While waiting, Doman can see the corpses of the men and women he has just killed. He can look into their frightened eyes which stare off blankly into infinity. He sees some of them are younger then him and he's barely a man himself. He questions what he has just done.
The engineer arrives and blows the door for them and takes up a rear position so they won't have to wait for him anymore. They begin another raid, this time Doman orders their weapons on stun and to take as many prisoners as possible, no matter how unimportant their victims are for questioning. The hard ass stormie questions his orders but reluctantly obeys.
By the time they get to the command center of the base, the hard ass has convinced some men to help him overthrow Doman for breaking some of their orders. Some join him, others team up with Doman.
That's all I got. I'd kill off Doman personally somehow just to make the story seem more real. He should maybe sacrifice himself for the Rebels after maybe talking to one of their prisoners face to face. Characterization is key if you want the reader to care the protaganist has died.
"The Force is strong with Katarn...." - Darth Vader, Star Wars: Dark Forces