Ordnance pod

The resupply canister is a United Nations Space Command rearmament capsule. Resupply canisters are frequently used to rearm UNSC ground units in hazardous combat situations.

Description
A resupply canister is a long, oblong capsule with a length of 2.76 meters (9.06 feet) painted in olive green drab. In the interior is a stiff blue or black/gray foam that encapsulates a firearm, typically an M7/Caseless Submachine Gun, BR55 Battle Rifle, M90 Shotgun, SRS99C-S2 AM, MA5C ICWS, or M19 Rocket Launcher. Pelican dropships may carry six resupply canisters on their tail assemblies and eject them in sequence, allowing the capsules to air-drop to the ground and implant themselves firmly into the ground, similar to the ODST Human Entry Vehicle. Upon impact, panels on the upper surfaces of the capsule pop off, revealing a partial profile of the weapon within.

There are at least three types of resupply canisters: The resupply canister Type-B Capsule, and the Resupply Canister Type-C Capsule. The Type-B Capsule was used in Halo 2, and the Type-C Capsule was used in Halo 3. The difference between Type-B's and Type-C's is that Type-B's lack the rounded part on top, the flashing red light, and the pop off protection panel. There is also a more streamlined variant of resupply canister that is commonly dropped by Longswords to deliver ordnance to ground forces.

In-game
They also appear by default on the multiplayer level High Ground and on Valhalla, having been dropped by Victor 398 before crash landing. In Forge, you can spawn the pods, but not delete opened ones. If one is spawned couple feet off the ground, the panel comes off but will spawn a full capsule.

M2859 Materiel Acquisition Pod
The M2859 Materiel Acquisition Pod or MAP, commonly referred to as "ordnance pods", are pods used for resupply by the UNSC. The M2859 MAP were developed by Misriah Armory. They are often deployed for UNSC forces deep behind enemy lines or outside the range of a forward operating base. They are fitted with weapons, explosives, and other military hardware launched from the air or suborbital positions. Most pods are saved for heavy materiel, munitions, and explosives, or long-range equipment.

Trivia

 * In the Halo 2 level Delta Halo it is possible to move these weapon capsules after they have been deployed by a Pelican by pushing them with a Scorpion or Wraith.
 * These pods can kill the player in Halo 2 if one stands right under them when they are dropped.
 * In Halo: Reach during the start of Firefight matches, a Longsword can be seen dropping ordnance pods that resembles a resupply canister (they usually contain heavy weapons).
 * In Halo 3 via Forge, players can embed them into the ground creating vehicle barriers.

List of appearances

 * Halo 2
 * Halo 3
 * Halo: Reach
 * Halo 4
 * Spartan Ops