Flak Jacket

Flak Jacket is a Tier 2 perk featured in Call of Duty: World at War and a Tier 1 perk that will be featured in Call of Duty: Black Ops, that reduces explosive damage done to the player. In WaW, it is unlocked at rank one in the "Heavy Gunner" class.

Description
Flak Jacket decreases all explosive damage taken by 0.75, and caps the maximum damage taken from any one explosive (excluding a direct hit from a grenade launcher, Bazooka or a tank shell) to 75. In effect, this allows the player to survive nearly any indirect explosive attack. Players who find themselves constantly killed by Grenades, Bouncing Betties, Tanks, Satchels, Artillery Strikes or M9A1 Bazooka will find this perk to be very useful. This perk has very little effect in Hardcore, due to decreasing HP of players, since the 75 damage cap is far above the maximum health level.

Tips
This perk is commonly used in Headquarters, Domination and War to prevent being killed by grenades while trying to capture a flag or HQ. It is also especially useful in Search and Destroy, as the enemy will plant Bouncing Betties on the target to kill the player planting the bomb. It can also be helpful when camping in the watchtower on Makin because players will often throw grenades into the tower in hopes of killing the player. It is often used with SMGs or Shotguns, as they can deal high damage even without perks such as Stopping Power.

Trivia

 * Blast Shield in Modern Warfare 2 when equipped obscures the players view and also protects the player against Stun grenades whereas in Call of Duty: World at War Flak jacket doesn't.
 * Although very helpful for surviving indirect explosions, if someone attaches a Sticky Grenade to them, the player will still die.
 * Elements of this perk are survived in the Blast Shield, a piece of equipment in Call of Duty: Modern Warfare 2.
 * In "The Ungroundable", (A South Park Episode) Everyone in the computer room is playing Call of Duty: World at War. Stan Marsh gets angry for not killing a classmate with a explosive because of the Flak Jacket perk, shouting "Ok, who's using the Flak Jacket cheat?", and his classmate answers "It's not cheating to level up!" Obviously the show writers haven't noticed the fact that Flak Jacket is unlocked at level 1, and Stan is clearly on a rather high level, since he uses FG-42 with a Telescopic Sight.
 * It cancels out and is canceled out by Fireworks just as Juggernaut gets canceled out with Stopping Power and vice versa.