As you fight your way to the roof of the building keep an eye out for this supply area. You'll find a bunch of supplies here and a Health and Ammo Dispenser.

When you reach the roof you'll encounter a few stealth units. There are also supplies in the bunker.

After you have eliminated all hostiles at the listening post, the Sergeant will let you know that the mission is complete. Even if you didn't bring the Sergeant with you, you'll still be transported back to the command tent in a few moments.

Shortly after ariving back at the command tent you'll get the quest complete message.