The Guns Of Anchorage Walkthrough - Fallout 3 - Operation Anchorage - Page No. 17
As you approach the third gun you'll be attacked by a few soldiers from inside the bunker. They are easy to dispatch with the Gauss Gun.
Inside the bunker itself you'll find a Health and Ammo Dispenser.
Once you have dealt with all hostiles, plant the explosive charge and take cover.
After destroying the third gun you'll end up standing around for a minute or two. The Sergeant will be quite happy with this situation.
Before long you'll be transported to the Field HQ where the General will talk with you and congratulate you on your success.
After your brief chat with the General, you'll get the quest complete notification.
