Iron Lungs

Iron Lungs is a Call of Duty 4: Modern Warfare and Call of Duty: World at War Tier Three perk that increases the time a player can steady a sniper rifle's scope from 4 seconds to 9 seconds. However, holding the rifle steady until the 9 second limit will cause the sniper rifle to sway uncontrollably, and will take 10 seconds before the sniper rifle can be steadied again, thus, it is reasonable to not steady your aim indefinably but just long enough to see a moving target. Iron Lungs is only used for sniper rifles without the ACOG scope attachment; it will not work for any other weapon, even with the ACOG scope attachment. In Call of Duty 4:Modern Warfare, the perk is unlocked at 26. In Call of Duty: World at War this perk is unlocked at level 60.

Iron Lungs is generally useless if Stopping Power is also being used or in Hardcore modes. It should only be used when going for headshots, which is only done for the sake of challenges or to ensure a one shot kill without Stopping Power. This is because snipers steady fairly quickly and any decent sniper will have more than enough time to set up a kill shot in the allotted 4 seconds.

Among other players, however, Iron Lungs offers a significant advantage when compared to other Tier Three Perks (most of which are more or less useless for a sniper). While 4 seconds is ample time to kill an individual target, most players will find themselves hard-pressed to successfully engage two or more targets before the allotted 4 seconds expires and the rifle sways uncontrollably. This particularly applies in such game modes as Headquarters where it is not uncommon to see the enemy team generally moving in a group (namely, towards the headquarters). Moreover, it should be noted that without Iron Lungs, the player's rifle will sway uncontrollably whenever the rifle is steadied for 3 or 4 seconds whereas with Iron Lungs, steadying the rifle for 3 or 4 seconds will not entail a significant amount of sway. With Iron Lungs, snipers who limit themselves to steadying their rifles for 3-4 second intervals will be significantly less affected by sway and will therefore respond much quicker to newly presented targets than their counter-parts who neglected to use the perk.

Trivia

 * In World at War, the image of the perk depicts a sniper scope over the lungs.
 * In Modern Warfare 2, this perk is replaced by the Pro version of Steady Aim.