It is used in the second part of the level "Rebirth" and, when the player controls Jason Hudson. When Nova 6 is released the player's current weapon will disappear, the mask will appear in the player's hand and is placed on the player's face. Likewise all the US soldiers put on their Gas Masks at the same time. The gas mask is removed once the player reaches the bio weapon facility. Note that when it is placed on the players face, the bottom right hand corner of the player's screen will label "Gas Mask" as a weapon. The mask will start to develop cracks depending on how much damage the player takes and will eventually break when the player dies. They will restart from the last checkpoint, but with a new Gas Mask.
No Leaks (50 / Silver Trophy ) Make it through the Nova 6 Gas without dying on Rebirth Island.
Call of Duty: Modern Warfare 3
Gas Mask is used in the Campaign, and once in Special Ops. In Campaign, it is seen in the mission Bag and Drag, being used by Frost and Delta Force operatives, as well as Russian Army. It is also seen in the mission Return to Sender used by Price, Soap and Yuri after setting off the gas canisters. Price gives one to Waraabe, shortly before killing him. In Special Ops, it is used in the mission, Toxic Paradise.
Chemical Agents also use Gas Masks as part of their equipment.
Yuri putting on his mask.
Call of Duty: Black Ops II
In the opening cutscene of Origins, several German soldiers are seen wearing gas masks.
The Gas Mask appears in the campaign level "Struck Down", where it is put on right after the player uses the Remote Sniper for the second time. The player then is able to use Tear Gas against the enemies, with the Gas Mask protecting the player and other Ghosts from its effects. It affects the player's HUD similarly to past games. The Gas Mask is removed after the Ghosts locate Ajax. In addition, gas masks are seen at the start of "Sin City", where Federation soldiers can be seen wearing them. In multiplayer, a Gas Mask is worn by the Maniac.
A gas mask worn by a Federation soldier in Homecoming.
Call of Duty: Black Ops III
The Gas Mask is a buildable feature in the Zombies map Zetsubou No Shima. Once equipped, players will not cough when entering a cloud of gas left by a spore. It will break once it has been used enough, although a fresh Gas Mask can be equipped once the old one is destroyed. Players can also use the Gas Mask to increase the amount of the time the player can breathe underwater.
The gas mask is comprised of three parts:
Mask cover: found near the green 115 lake.
Mask strap: found near the Propeller Trap.
Breathing tube: found near the docks.
Call of Duty: Modern Warfare & Warzone
Various Gas Masks are present in Call of Duty: Modern Warfare and Warzone.
In multiplayer game modes, various skins for Domino, Grinch, Otter, Mara, Minotaur, and Krueger include Gas Masks. Various identity items, as well as the "Gas This!" charm, are also available and depict Gas Masks.
The Gas Mask is a piece of equipment found in the Battle Royale game mode of Warzone. Once equipped, it will allow the player to survive in the gas for 15 seconds without taking damage. The Gas Mask is dropped upon death.
/ Silver Trophy 
) Make it through the Nova 6 Gas without dying on Rebirth Island.
