Deployable cover

The Deployable Cover is a new piece of Covenant Equipment introduced in Halo 3.

Overview
This piece of Equipment is similar to the Stationary Shield Generator seen in Halo: Combat Evolved and Halo 2, except now it is mobile.

Additionally, the shield operates as a "one-way" shield, i.e.; the user is able to fire through the shield from behind it with projectile weapons, but any bullets and other solid projectiles (except Carbine and Needler rounds) coming from the front will be deflected, however plasma fire and Spartan Laser weapons fire are stopped by the shield from either side. However, the Spartan Laser goes through the bases of more than five deployable covers, assuming they are lined up close together. The user is given an enormous tactical advantage in exchange for being exposed from behind and to the left and right, so it is wise to deploy it towards your main threat, whereas the similar Bubble Shield provides complete 360 degree cover, but cannot be fired into or out of.

The shield is deployed in the same manner as all other equipment in the game, and it will stay activated until it takes enough damage, or if left untouched for too long. The shield's health is represented by its color: it is normally blue, turns red/orange as it is damaged, and finally deactivates. If left alone, the shield will regenerate to full health. To deactivate the shield permanently, the base must be destroyed. This only works in campaign. In Multiplayer, the deployable cover will self destruct after 30 seconds. It is also possible to make a "bubble" from two of these shields.

Like the Portable Gravity Lift, the Deployable Cover, when activated, will be destroyed after a fall from a great height.

Glitches
One of the most popular glitches that is used with a deployable cover is the HEV crate glitch. This glitch essentially allows the player to permit temporarily, creating a sort of HEV. It is used in conjunction with a Gravity Lift and an open-ended crate. What you must do is find an open crate and place the gravity lift inside and then get the deployable cover and then throw it on top. The gravity lift will then lift up the deployable cover which in turns pushes on the crate and causes it to fly into the air. It may take a couple of tries to get this right and the only reasonable way you can pull this off is by arranging it on Forge or having a partner. The crate will fall when the gravity lift runs out, but firing from in here gives a good battle field vantage point and the player is only truly vulnerable to explosions. When you're against a Scarab and it's about to explode, put down a deployable cover to protect you from the explosion. Unlike the bubble shield, if you are behind the deployable cover flying debris from the exploding scarab will just bounce off leaving you protected.

The Machine Gun Turret's rounds seem to be able to pass through the Deployable Cover. This can be done in the level Crow's Nest. In the hangar, many Deployable Covers can be found. Pick one up. When you reach the Drone fight, go to the turret and throw the Deployable Cover in front of the turret. The turret's rounds will pass through the Cover, and the Drones won't be able to see you.

Trivia

 * Most projectile weapons that are not plasma based can shoot through the back of the Deployable Cover.
 * Deployable cover is often used as an area to jump off of, as it is easier to use than the grenade jump for some players. One of this tactic's best uses is to get both of the skulls from the level The Ark (level), Famine and Catch, in Halo 3.
 * The only map the Deployable Cover isn't available in Forge Mode is Sandtrap.
 * In Campaign mode, the Deployable Cover is completely immune to the projectiles fired by Flood Ranged Forms making it very useful on the eighth level of Halo 3, Cortana, especially on higher difficulties in places with little cover.
 * When the Deployable Cover has undergone tons of damage (Changing from Blue > Orange > Red, the best way to do is to melee), you can just shoot through it as it will collapse thus injuring the enemy hiding behind it. After you leave it for a while, it will go back to blue and will not permit you to shoot through it once more.
 * Enemies cannot detect you through a Deployable Cover even on the highest difficulties, so you can just watch your enemies stand there while you pick them off with a Battle Rifle. This can be especially helpful on the part of Crow's Nest, where you have to battle eight Brutes and a Chieftain, since there are plenty of Deployable Covers around.
 * It's possible to gather enough Deployable covers (like in Forge) and create a makeshift but stronger imitation of a bubble shield that does not cover the top, allowing people to possibly jump over.
 * The Deployable Cover is banned from matchmaking along with the Radar Jammer and Flare.
 * Standing on a Deployable Cover after it has been broken will cause you to fly across the map when it goes back up.