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 mancannons 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, 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 mancannon 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 and Narrows, but similar devices (these are called Grav lifts) can be found on Guardian and Epitaph. 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 dont have the time to make the difference between the two of them

Portable Man Cannon
The mancannon only appears in 2 maps so far, Valhalla and Narrows. A portable version of the mancannon 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 mancannon is also an object which is immovable after being placed in Forge. Unlike the small Portable Grav Lift the mancannon can't be destroyed.

Tactics
The main mancannon 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 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.

Trivia

 * Almost anything can be sent through the man cannon. This includes the flag in a game of CTF.
 * In RVB (Red vs Blue) it was called the "Grif cannon", The name comes from Sarge who never ceases to show his hate towards Grif
 * The mancannons 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 mancannon. If the round or game is ended the map is no longer overloaded and thus, activates the mancannons again.
 * The main difference between a grav lift (for example the one on Colossus) and a mancannon is that it is more powerful and at a more horizontal angle. However, the main grav lift on Epitaph can not be called a mancannon because it doesn't look like those present on Valhalla and Narrows. It also makes a different sound when used.