Continue to fight your way through to the Lambda Complex. The military are preparing to withdraw and level the place with airstrikes. If you can find the controls you may be able to use the airstrikes to your advantage by reprogramming the co-ordinates.
Watch out for Xen soldiers, they are deadly and hard to kill and are sometimes dropped in by Xen dropships.
Find the security guards and keep them alive as you will need them to open locked doors for you.
This mission is based on the original Half Life level Surface Tension.