Seamus on his own initiative readied the particle cannon and provided supporting fire as needed.  While he was aware of critical targets, he was also aware of drones, gunships, and even infantry with power armor as he scanned the area his allies were engaging.  "Providing covering fire.  I have the range."  While he was careful not to shoot the hostages or the ship his allies were boarding on, he made sure that the drones, gunships, and power-armored infantry did not down his allies.  

Full power was on his primary weapon.  Seamus also readied the plasma ball launcher just in case.  The missiles were for now not engaged as at the range he was in would not warrant a barrage of missiles.  Though if more powerful enemies were there, he'd attempt to close the gaps to maximize the payloads.  Bringing heavy weapons to the table was a wise move for now.