Flank the turrets and shut them down | Mission 2: Battle for Sulaco A: CM Guide
Last update: 11 May 2016
There are two turrets in the closest area. The left corridor leads to the first. When you reach the fork, don't turn right, but go to the left room. Kill some mercenaries which will surely show up, and go around the back of the turret to disable it (the above screenshot).
The second turret can be reached through the corridor to the right of the screening room. Similarly, it's not recommended to try to approach it in a straight line (through the server room), but going around it on the right (the above screenshot). It's worth adding that for the task to be completed you only need to disable one turret, but of course, it's better to deactivate both.