An oxygen tank, sometimes referred to as oxygen cylinders due to their shape, is a specialized tank containing oxygen used primarily for breathing underwater. It is often used by the military for underwater insertions, although it can also be used for mental recuperation for elderly citizens.
Outer Heaven and Zanzibar Land used oxygen tanks that were presumably used for work relating to waterways. Solid Snake, during the Outer Heaven Uprising and the Zanzibar Land Disturbance, made use of these during his missions after procuring them.
The lifeboats of the USS Discovery contained oxygen tanks so that it could supply even the ones not outside the boat with oxygen to ensure everyone's survival.
Solid Snake also used an oxygen tank during the USS Missouri briefing during the Guns of the Patriots Incident, namely as a means of recuperating after his battle with Liquid Ocelot and his nearly being killed by Outer Haven.
Behind the scenes
- "Oxygen Cylinder
Using the oxygen cylinder in the water will preserve your LIFE gauge."
- ―— O2 Cylinder description in Metal Gear
The oxygen tank was an item used in the MSX2 games, and was the only thing that allowed the player to access the second part of Building 2 in the player, as it had a large part of the base was separated by a large and deep waterway.
In the non-canon sequel Snake's Revenge, the oxygen tank returns, this time as a renewable procurable item akin to the rations, grenades, and ammunition boxes. These were used for the side-scrolling portions of the game, and a maximum amount of oxygen tanks are especially needed for the final side-scrolling portion of the game.