The mission starts with Darth Vader ordering Magma Troopers to wipe out the Rebel Forces. They proceed to send a prepared AT-ST to deal with the job. During the first cutscene a Magma Trooper in the background bumps his head on a staircase, which is a reference to a similar incident in A New Hope when a Stormtrooper bumps his head on a door frame in the Death Star.
Upon exiting the hangar, there are several bunkers that Rebels pour out of to attack the AT-AT. Then A-Wings attack the walker followed by X-Wings. Then additional Rebels come out of bunkers. Finally, Rebels swarm out of their base to attack the walker.