Deep Impact

Deep Impact is a Call of Duty 4: Modern Warfare and Call of Duty: World at War perk that gives a player increased bullet penetration. The exact effect is that bullet damage is only reduced by half of what it normally is. This allows users to lose very little damage when shooting through thin materials, while also allowing them to shoot through materials that normally cannot be shot through. It also allows the user to penetrate walls from more angles. Deep Impact does not increase bullet damage to an exposed enemy. Deep Impact also does not give players the ability to penetrate every material.

Deep Impact doesn't reappear in Modern Warfare 2, but FMJ fills it's place; similarly reducing damage reduction of shooting through surfaces.

Additional Multiplayer Tactics
Deep Impact is a favorite among snipers and light machine gunners. It can also be very effective with players who can expertly read the minimap and know common hiding spots that are behind cover. It can be used to take out players behind most materials at long ranges or clear a room/hallway without ever entering it. Learning how the players use cover and keeping an eye on the map can provide an easy target. When fighting from a window it is smarter to move to the back wall or leave the room completely. Remember that crosshairs will provide a hit indication so if a player is stuck behind an object it may be better to get up and make a break for it.

This perk can also be used to more efficiently dispatch enemies only partially behind cover and would normally be very hard to hit as they would be too small of a target, and as such is a very good complement to high recoil weapons such as Light Machine-Guns and the M14. Deep Impact is also extremely effective on SMGs in Hardcore (besides the AK-74u), as they have low wall penetration, although using this perk with the "spray and pray" tactic is frowned upon.

This perk is also very effective in the World at War map "Makin", and "Makin Day", in the raised building (some call it the tree house), for the enemy has nowhere to run except behind thin grass walls.

There are certain challenges that can be completed easier, like "X-Ray Vision", with the help of this perk.

Trivia

 * The perk icon shows not only the bullet piercing a surface, but also the cartridge still attached to the bullet. this would be impossible in reality, as the bullet is propelled by the gases created by the gunpowder in the casing.