One Man Army (sometimes abbreviated as "OMA") is a Tier 1 perk available in the multiplayer of Call of Duty: Modern Warfare 2. It allows the user to switch classes without needing to respawn. However, as a downside, it removes the user's secondary weapon. The perk is unlocked at level 45.
There is a five second waiting period during which time the player can only move, crouch, jump and prone. When the player switches from their primary weapon to the backpack, it brings up the class menu. From there the player can pick the class desired to switch to. Users can switch to the same class repeatedly, or through several different classes with One Man Army.
One Man Army Pro is unlocked after a player has received 120 kills while using the One Man Army perk. One Man Army Pro reduces the time required to perform the class change to three seconds.
Although many players use the perk to resupply ammo for weapons, especially Grenade Launcher grenades, One Man Army was intended for more tactical gameplay. For example, one could switch to a Cold-Blooded class when the enemy has air support up, or Hardline to acquire a killstreak early, or Danger Close Pro to increase killstreak damage. A player could effortlessly switch to any of these classes for almost any different weapon. Switching classes with One man army causes the player to be completely defenseless so using it under the cover of teammates can allow you to safely switch classes without getting killed by other people.
OMA is often used with an assault rifle with an underslung Grenade Launcher, as well as Danger Close, to have an infinite supply of extremely lethal Grenade Launcher rounds. Danger Close would increase the blast radius of the grenades, and OMA would resupply the rounds.
Another fairly common tactic is to use OMA with one of the belt-fed light machineguns (RPD, MG4, or M240) and switch classes whenever the player needs to reload. The three second time it takes to switch classes with One Man Army Pro is significantly faster than performing the normal reload animation for these weapons, even if Sleight of Hand is used.
- A One Man Army pack is visible during the mission "S.S.D.D." in the makeshift basketball court, underneath the Humvee being repaired, near the first intel item, and at the "door" of The Pit.
- When the player switches between classes with One Man Army, their character model changes with it.
- One Man Army cannot be used to repair a Riot Shield.
- In Terminal, if the player kills one of the Russian police with a Riot Shield, a green bag that looks like the One Man Army bag can be found.
- On the back of the One Man Army bag, the letters "OMA" can be seen, along with "No Scope."
- In the Spanish version of the game the perk is called "Camaleón" which in English means chameleon.
- If the player takes One Man Army off of their class, the default secondary is the G18.
- In Modern Warfare 3, the challenge for getting the Specialist Bonus is called "OMA".
- On the Modern Warfare 3 DLC Faceoff maps Lookout and U-Turn, there are OMA bags scattered across the map. On Lookout, there are One Man Army bags around the Delta spawn. On U-Turn, on the M1A2 Abrams tank on the south of the map, there are OMA bags strapped to the side of the tank.
- C4 or Claymores planted before one uses OMA will not disappear and can still be detonated by double tapping the reload or use button.