The aim of this challenge is to complete a
Main mission of MSGV without triggering Reflex Mode,
or entering Combat Status.
The easiest mission to do this in is in
Prologue: Awakening. The only place you are able to break stealth is in the Foyer, before you meet up with Ocelot. You can also work towards the achievements:
When you reach the foyer,
DO NOT go down the stairs. Instead, crouch using
, and creep around the corner, sticking to the left hand wall, until you see an opening in the barrier. Go prone by holding
, and wait until the enemy near you has its back to you. Crouch using
again, then drop down onto the floor. Once you land,
IMMEDIATELY go prone, and slowly move towards the exit. After the ensuing cutscene, there aren't any enemies left! Follow the mission as normal, and once completed, you should unlock the achievement.