Boarding is a technique featured in Halo 2, Halo 3, Halo 3: ODST and Halo Wars. It is a unique and interesting way of neutralizing an enemy vehicle by stealing it from its current pilot, and then taking it over.
Boarding, also called carjacking or hijacking, is the process of forcibly ejecting a vehicle's pilot and proceeding to take over the vehicle and use it against them. It is accomplished simply by holding X in Halo 2 or RB in Halo 3 (default controls) when near an enemy vehicle.
The main difficulty in boarding a vehicle is getting close enough to board it: a player attempting to board a vehicle can get splattered or killed by the vehicle's gunner. If the player succeeds, however, they will have disarmed their opponent and earned a free vehicle for their trouble, thus making it worth the risk. Players who succeed at boarding should be careful, as the other player may be able to re-board the vehicle.
In Halo 3, when ejecting an enemy driver, the melee attack that takes place as you eject them severely damages the enemy and may even kill them if their shields are down. After being successfully boarded, there is a brief period of time when you are stunned and your moving speed is greatly decreased. If you are being boarded it is impossible to dismount the vehicle and try to escape -- you are trapped inside until you are killed, ejected from the vehicle, or until you kill the hijacker (by destroying the vehicle or forcing the hijacker into an obstacle). This was not true in Halo 2.
Boarding is most often done on Banshees, Ghosts, Hornets, and Brute Choppers. The act begins with an animation in which the attacker jumps on top of the victim's vehicle and forces the victim out. The attacker then enters the vehicle and takes control over it. Ghosts and Choppers are the easiest to board because they only have forward firing guns, leaving them vulnerable from all other directions.
Boarding a Warthog, Spectre, or Prowler is different in that an attacker will still eject their victim, but without taking his or her seat. This can be dangerous as the player that was boarded can start shooting the attacker while the attacker is still returning to first-person view.
These vehicles also have turrets, making it difficult to get close enough to board them, and leaving an attacker vulnerable to fire from the turrets while boarding. These vehicles can still be neutralized by boarding them, however; ejecting the driver leaves the gunner a sitting duck, and ejecting the gunner makes the vehicle less dangerous.
In battle, it is possible to board the passenger seat of a Warthog, emptying it; from there, you can enter the Warthog and melee the driver to death. You will, however, have to hop out and circle around the vehicle to take control of it after you kill the driver.
Boarding works quite differently on Scorpions and Wraiths. The attacker does not eject the victim or take their seat. Instead, the boarder jumps onto the target vehicle. From that position, they may melee the vehicle -- exposing and eventually killing the driver -- or they may plant a grenade, killing all occupants, destroying the vehicle, and, in Halo 2, endangering themselves.
A Scorpion or Wraith's gunner can fire upon any players that attempt to board the vehicle; for this reason, attackers should make sure to kill the gunner before boarding the tank. Scorpion/Wraith boarding is different in every game. In Halo 2 you have to melee the hatch off before planting a grenade and the person being boarded can jump out. In Halo 3 both attacks are much faster, the grenade can be shoved through the hatch, and the occupant is trapped in the vehicle. Halo 3: ODST is the same as Halo 3, although the distance from which you can board seems to be larger.
In addition to the typical method of boarding Campaign Wraiths, Halo 3: ODST has another. This procedure is almost identical to the normal one.
The player should perform the typical method as normal, though it should be noted that they have to time the actual entry of the vehicle properly. The trick is that the player must enter the vehicle the moment "Hold RB to drive Wraith" appears -- but since this is extremely difficult to time, the player must hold the button before the message appears.
Notably, boarding and re-boarding the same Wraith can cause issues. In some cases, if a player has boarded the same Wraith several times, they may die when they attempt to drive it again. The fix is to quit to the main menu and resume from the last checkpoint.
Halo 3's Mongoose cannot be boarded; however, a player may melee the driver off as they pass by. Alternatively, an attacker can enter the rear passenger seat of a target's Mongoose and then kill the driver with a few quick melee attacks or shots to the back of the head, although such a maneuver would take almost perfect timing and precision.
A player can indisputably avoid being boarded simply by constantly moving at full speed, sometimes even scoring some splatters along the way. However, if a player voluntarily exits the vehicle before they are ejected, they may be able to re-board the captured vehicle. Additionally, if you are boarded while inside a Banshee, a maneuver called "The Great Banshee Switch" can be used to recover the vehicle.
If you are willing to sacrifice the vehicle, simply throw a Plasma Grenade right when you are boarded. It will destroy the vehicle and kill your attacker, but you will also die in the explosion. Alternatively you can drive off the map before your opponent hijacks you(works on maps like Standoff and Avalanche, causing your would-be hijacker to fall to his/her death as well as yourself.
In Halo 3's Campaign, if a Brute boards your Wraith, you cannot leave the vehicle to escape being beaten to death. However, you can just fire the main cannon, which will damage the Wraith but kill the Brute.
If an enemy boards a small vehicle such as a Ghost, you can boost toward a cliff. If you time it right, you will be kicked off your vehicle and the enemy will go off the edge.
It is possible to splatter a boarder after they are on your vehicle. Simply smash them against a wall.
Here is a list of characters that can board vehicles:
A Spartan getting ready to eject a Ghost's pilot.
A Spartan hijacks another Spartan from a Ghost.
A Spartan ejects a rival Spartan.