Throughout the game, there are several instances where you're forced to use a specific weapon in order to proceed. For obvious reasons, these weapons are allowed to be used for their intended purposes in the "Sidearms Only" and "Standard Loadout" categories. They include:
-The mandatory turret sections in the missions "Under NORAD's Nose" and "Memories."
-The Anti-Tank SMAW used to destroy the tank in the mission "The Trojan Horse."
-The EMP Grenades used to kill the armored enemies and Singularity in the missions "Red Section," "Drowning," "Event Horizon" and "Matter's End." (EDT Darts are NOT allowed to be used in place of these grenades in "Sidearms Only," but CAN be used in "Standard Loadout.")
Using the weapons listed above for anything other than their intended purposes will invalidate your run. Use of other weapons not classified as "sidearms" or "standard loadout" will also invalidate your run.