Deployable lookout tower

A Deployable Lookout Tower is an anti-gravity-operated tower in use by the Covenant. They are mainly used to fortify specific areas on a battlefield.

Summary
A Deployable Lookout Tower is comprised of a circular base, in the middle of which an anti-gravity generator is placed. The circular platform is suspended in the air, given the anti-gravity power by the generator. The platform also has a gap in the middle for the ferries to be transported. The anti-gravity generator works just like a gravity lift, transporting supplies and troops freely. It also has the same color as the gravity lift.

The perimeter of the base is comprised of three ramps, and three pillars, probably put there for extra protection. They are all placed in a motif (one ramp-one pillar). The platform has also three protective pillars and large gaps between them. The pillars are taller and thinner compared to the ones of the base and the gap between them is bigger. The gap is used for snipers to have a clear line of sight and for gunners to place their Plasma Cannons. Some Towers' platforms, instead of the usual oval pillars, have three thinner, longer pillars that support a rooftop-like cover.

The base, when placed on the ground, can not be moved again. The platform, however, is not as steady as the base and a single shot from heavy weapons, such as the Rocket Launcher, the Fuel Rod Gun from a distance and the Shotgun from nearby, will make it lose it's balance and it may fall off. Three shots from the Rocket Launcher are sure to make it fall.

The tower is able to garrison a whole File, but usually single Jackal Snipers, Brutes with Carbines and Heavy Grunts will occupy it.

In-Game Appearances
In Halo 2, the platforms are destructible. The player can climb on them by the anti-gravity lift, and he/she can use it just like any Covenant. However, his/her position becomes highly exposed then. They appear in numerous Campaign maps as well as in the multiplayer map, Relic.

In Halo 3, they are destructible again. They are also able to be climbed and appear in some Campaign levels.

In Halo Wars, they are deployed by the Covenant, but once every single Covenant troop on it is killed, UNSC soldiers can garrison in it, increasing their combat capabilities. A Covenant File is usually found on top of them defending the Jackals and Heavies there. In multiplayer, they are left neutral for either team's taking, providing a useful defense, if needed, plus they will not be destroyed no matter how many times a marine hits it.

In Halo 3: ODST, many are seen deployed in New Mombasa.

Glitch
On all Halo 2 gravity towers that have been knocked down, the base is still active and can be used to push you up directly into the air. From this position, you can continue to hover and snipe enemies. This glitch is absent from Halo 3; once the tower is destroyed, the gravity lift of the base does not work. However, the tower itself (if still intact) will push you through the hole in the center, as if the gravity lift was under it. This is most likely a design shortcut; placing the lift on the tower ensures that once the tower is destroyed, the lift would also be disabled.

Trivia

 * Halo 2 is the only game in the trilogy to use Deployable Lookout Towers in multiplayer. The tower can not be destroyed but it can be shot off.
 * Tags for Deployable Lookout Towers (and Shades) exist in Halo 3 's Snowbound. The Towers can be manipulated in Forge, but have no names, costs, or maximum limits. The tops of the towers tend to spontaneously disappear, and do not respawn.
 * If the top part of the tower is flipped upside down while a Grunt is on the Plasma Turret, the Grunt will keep firing normally.
 * In Halo Wars, they are referred to as a "Sniper Tower".
 * Also in Halo Wars, when garrisoned with Marines, one will take cover at each of the fins and will blind fire at enemies.
 * In Halo 3 and Halo 3: ODST, if you can detach a tower with Plasma Cannons from the base without destroying it (use a Gravity Hammer), and if the tower is tilted more than 45 degrees, a message saying "Inoperable turret" will appear when the player is near the turret, even if Grunts are still manning them.