Initiate the bunker lockdown procedure | Mission 12 - Site F Splinter Cell: Blacklist Guide
Last update: 11 May 2016
Hide behind the desk with terminal C on it and wait for the terrorist from this room goes left again. Return to the previous room but, don't enter the shaft this time and go left. After you reach a well-lit corridor, take the first turn to the right and approach the entrance of the ventilation shaft shown in the screenshot.
After you lift the shaft's grate, take a few steps forward and jump down to a lower portion of the underground structure. You only need to go ahead now and interact with the last terminal marked by the game. This will initiate the bunker lockdown procedure.
You will soon see a longer cutscene, during which you will receive a reward for the recent neutralization of the high-value target (up to 30 thousand dollars). The cutscene featuring the captured Briggs includes two interactive moments and the thing is straightforward because you simply need to press the melee key/button at the right moments and, you don't need to hurry with that.