M9 fragmentation grenade

The UNSC-issued M9 High-Explosive Dual-Purpose Grenade (abbreviated M9 HE-DP Grenade), also known as the Fragmentation Grenade, functions in a manner very similar to contemporary hand grenades. A blast bursts the grenade's shell open and sends many small metal fragments flying at high speed, causing damage to Energy shields, armor, and flesh in a nine meter (30ft) radius. Four may be carried at a time, although this was reduced to two in Halo 3 due to the 4 grenade types.

Description
HE-DP stands for High-Explosive Dual-Purpose. The first phrase indicates the grenade uses a high-explosive substance to propel its shrapnel when the grenade explodes, while the second means it can be used against both infantry and vehicles (hence "dual-purpose").

The grenade has a hard metal casing that is smooth in Halo: Combat Evolved, but has a gridded surface in Halo 2 and Halo 3. This griding is most likely used to provide a better grip for the thrower, and contrary to popular belief, would not influence the fragmentation pattern of it's shrapnel. Instead, the grenade's outer metal casing, presumably made of steel or another metal (such as tungsten) or an alloy, would be blown to pieces when the HE core inside detonates.

AP FRAG can be viewed on the Halo: Combat Evolved M9's olive casing. AP most likely stands for "armor piercing", indicating the shrapnel of the grenade can penetrate lightly armored infantry.

In all Halo games, the grenade must first hit the ground before exploding. In Halo 1, the grenade would not detonate mid-air. In Halo 2 and Halo 3, it would bounce and explode mid-air a moment after bouncing. This presumed to be a safety feature, ensuring the grenade would only explode after striking a surface after being thrown, and not in the user's hand.

This may explain the lack of a "spoon", or handle, on the Halo 2 and 3 M9 HE-DP grenades. The spoon is a device that is gripped while the grenade is being primed, and ensures it will not explode until after the spoon is released, as it starts the fuse of a grenade as it flies through the air after it is thrown. In Halo 1, the spoon would have negated the need for this Halo 2 safety feature.

It is unknown how the M9 is first primed, but references to pulling a pin on the grenade is mentioned in the Halo novels several times, even though no pin is visible in gameplay. However, pulling a pin would require two hands, but each version of the grenade has a button on it's body. This would most likely be pushed to prime the M9 before tossing it. The pin reference is most likely an inaccuracy on the author's part in the novels, or perhaps just a turn of phrase that has lingered from more primitive grenade types.



Advantages
This grenade can be bounced around corners and travels farther than the Plasma Grenade. It is also harder to see and has a shorter fuse, therefore making it harder to avoid and more useful for killing enemies on foot. It also seems to have a larger blast radius than a plasma grenade in Halo: Combat Evolved. It has a further casualty range than the other grenade types in Halo 3.

Disadvantages
Unlike the Plasma grenade, this grenade doesn't stick to objects, making it harder to hit vehicles. It deals slightly less damage than the Covenant Plasma Grenade and Spike Grenade. Since it is harder to see, running over one by accident can happen more easily than with a luminescent plasma grenade.

Campaign
The M9 HE-DP Grenade is best used when enemies gather together in tight groups. A well thrown grenade placed in the middle of a squad of Elites and Grunts will kill most of the Grunts and damage the Elite's Shields. However a single grenade cannot kill even a Minor Elite but just damage its shields, the only Elites that can be killed with one is a Stealth Elite. Grunts may also panic and flee making them easy targets for follow up attacks. Frag grenades may be used against Jackals as their Shields will not protect them from the blast. The M9 HE-DP Grenade is also commonly used to disable most land vehicles with the exception of tanks.

Multiplayer
A multipurpose weapon, the fragmentation grenade can be used in corridors to flush out occupants. The blast will severely damage player's Energy Shields allow for easy follow up attacks. If lobbed under a vehicle, the explosion will either kill or severely injure the occupants. If timed correctly, grenades can be planted in the path of an oncoming vehicle. Most drivers will not be able to react quickly enough, and will most likely be caught in the blast. If you place the grenade under an enemy it will kill them. Note: this is very hard to do and it only works in Halo 2. Another good multiplayer tactic is to throw one at your feet while backpedalling when an enemy is charging at you. When the grenade detonates, the other person should be in the blast radius of the grenade and be killed; if not, use a headshot on them as their shields should be down. It can be done with other grenades, but as the frag grenade is the hardest to see, it is unlikely that the other person will dodge it. This is easiest done in Halo: Combat Evolved. In some maps like Snowbound and Sandtrap, if a frag is thrown it will stay where it lands. This is useful to fight oncoming traffic.