Immediately upon unlocking the Airlock, you will trigger a massive Zombie Horde that appears after a short period of time. It will mostly contain several rushes Zombies with waves of Hulks to absorb Gauss Rifle fire. Gargoyles will attack from above to limit the flamethrower's effectiveness.
Many players prefer to hold the high ground left of the entrance, forcing the enemies to take a longer approach to reach them. However, because the Civilian Escort will expire if not activated quickly enough when playing on Normal or Nightmare more aggressive teams will hold the lower level. These teams often fight the hordes up close and personal, relying heavily on the Flamethrower MK-3 and defensive skills. Towards the end of the horde a large pack of Agrons will attack, and must be quickly dealt with. Occasionally this Agron group is replaced by a large swarm of Seekers that attack much earlier. They are far faster and arguably deadlier.
After clearing out the Airlocks, General Koller informs Easy Company that thermal imaging detects a large concentration of heat signatures still in the airlock. He then informs Easy Co to investigate.