Man cannon

"The Homo Sapien Propulsifier, otherwise known as the Man Cannon" -Sarge

"It fires men?" - Pvt. Simmons

"Yes, and also Grifs. Come here, Grif." -Sarge

-From Red vs. Blue Beta Complex special

The Man Cannon is an object introduced in Halo 3 that tosses a player through the air to another part of the map. It works quite the same as a grav lift present in maps like Colossus and Lockout, the only difference is that the man cannons are somewhat more powerful and tilted at such a horizontal angle that you can easily overcome a large part of the map. The user is unprotected while in mid-air, but can still attack other players. It is much like the Covenant's Gravity Lift technology, so possibly the Covenant learned this from the Forerunners.

Function
While the name specifies a man, the cannon will launch anything that enters it. Unfortunately, its strength will be diminished when heavy objects such as the Warthog drives through it, and the cannon will not launch them as far.

As shown in the new Halo 3 Vidoc, Is Quisnam Protero Damno, Bungie created the Man Cannon to replace the teleporters because it adds far greater challenge and risk to the gameplay.

Bungie stated the following about the teleporters

"Although it was a great way to get around quickly, it didn't provide as much inherent danger as the man cannon does" -David Candland, interface designer at Bungie

The danger of using the man cannon is that your trajectory is set when you enter. Since you don't have a lot of air control, an enemy sniper will be given a good amount of time (the main man cannon on Valhalla takes ±2.5 seconds from 'take-off' to 'landing') to estimate where your head will meet his crosshair.

It also adds some advantage, as this player still can attack the other competitors. The player also has a quick overview of the positions of enemies and the current battle situation

Appearances
As of now, this device has only been featured in the Halo 3 Multiplayer maps Valhalla, Guardian, Narrows and Avalanche as well as a placeable object on Foundry, Rat's Nest, Standoff, BlackOut and Avalanche, but similar devices (these are called Grav lifts) can be found on Guardian and Epitaph, as well as a placeable object via the Forge in almost any other mulitplayer. The Halo 2 Multiplayer Maps Desolation, Ascension, Gemini, and Colossus also have Grav Lifts. Ivory Tower and Headlong also have lifts, only these are called 'air vents'. Most people do however still refer to them as grav lifts. Probably because in the midst of battle you don't have the time to make the difference between the two of them

Portable Man Cannon
The man cannon only appears in 4 maps so far, Valhalla, Guardian, Avalanche, and Narrows. A portable version of the man cannon can however be placed manually in Forge. This however, only applies to the 3 new maps featured in the Heroic Map Pack. (Rat's Nest, Foundry and Standoff)

This portable version has roughly the same 'firepower' but can be placed anywhere on the map on different angles. This gives the users of Forge endless variaties of fun and nice gameplay. The man cannon is also an object which is immovable after being placed in Forge. Unlike the small Portable Grav Lift the man cannon can't be destroyed.

Tactics

 * The main man cannon on Valhalla has a 'landing zone' roughly the size of an 'Elephant' Behemoth-class Troop Transport, but a good player will quickly see where his oppponent is about to land. This makes it easy for the enemy to throw a frag grenade or a Plasma Grenade right where you land, quickly scoring an easy kill. This is especially easy on Narrows since the landing zone is as small as a warthog.
 * Throwing a grenade (Plasma Grenades work best) or Power Drain on the man-cannon will turn it into a home-made mortar launcher.
 * If you are in the Coastal Base in Valhalla and you use the Man Cannon, you can actually jump across the river from where you land, with at least some momentum left from your launch. You must land pretty much on the edge of the land before you would fall into the river, if this can be done right, it may be helpful to get closer to the Spartan Laser on the hill.

Trivia

 * Almost anything can be sent through a man cannon. This includes the flag in a game of CTF.
 * In RvB (Red vs Blue) Sarge say the it can be used to launch dead men at a coordinated attack from the enemy, and "When no soldiers are available, use Grifs!", mocking Grif, as he always does.
 * Also in RvB, it is called The Homo Sapien Propulsifier by Sarge.
 * The man cannons placed in Valhalla and Narrows can be shut down if you use the map Overload Glitch. This makes it a lot easier to place objects such as spawn points, grenades and teleporters close to or even on the man cannon. If the round or game is ended the map is no longer overloaded and thus, activates the man cannons again.
 * The main difference between a gravity lift (for example the one on Colossus) and a man cannon is that it is more powerful and at a more horizontal angle. However, the main grav lift on Epitaph can not be called a man cannon because it doesn't look like those present on Valhalla and Narrows. It also makes a different sound when used.
 * Notably, in the popular real time strategy series Command and Conquer, it has been recently alluded that a vehicle (Bullfrog Attack Unit) in the upcoming game: Red Alert 3 will make use of a "mancannon" to propel infantry. At the very least, this could be a reference to the popularity of the cannon among gamers, in comparison to the teleports.