Armory A-01

Armory A-01 is a generic United Nations Space Command term for any armory and armor testing facility on the port side of an Orbital Magnetic Accelerator Cannon Platform.

Cairo Station Armory A-01
Cairo Station Armory A-01 was the United Nations Space Command armory on the port side of Cairo Station. During the First Battle of Earth, Covenant boarders invaded. Stealth Elites armed with Plasma Rifles killed the Master Gunnery Sergeant, who was equipped with a shotgun. SPARTAN-117, from Hangar A-02,wasn't able to get to him in time (as the doors on the floor would not open), but was able to avenge him.

actually if you play on heroic and take the left passage that leads to the armory from the hangar and kill the grunts on the right with a plasma and the ones on the right with a br and take the walkway on the right and once through the door below the armory take the left staircase while ignoring the elites attacking you the door should open and you should be able to have enough time to kill the elites attacking GUNS and save him but sadly he will either die from delayed attacks like in halo 1 where they die if nothings there or he will get killed by the stealth elites but if you find a way to kill the stealths in the basement without stopping you can save him only for him to die by plasma cannon fire. im am not sure if you need to follow the steps but that is what i did.

Weaponry
Armory A-01s main stored weapon are SMGs; there are roughly a dozen SMGs, most in collapsible racks along the main wall. On the left hand table, there was a Battle Rifle, a Magnum, and three packets of Battle Rifle ammo. On the right hand table, there was three boxes of shotgun shells, plus two packets of SMG ammo. The far right side table has a medical box that is labeled "Rescue".

It is quite possible that the Armory A-01 had a larger complement of BRs, Mags, and Shotguns, but these were taken by Marines to help defend Cairo Station. Due to the Fact that some SMG racks were empty only reinforces this claim. The Armory might have also been used to fix and clean weapons, and house some medical supplies. Since there are numerous racks of SMGs and BRs all throughout the station, Armory A-01 may have been used to store a larger number of weapons, plus much ammunition.

Energy Shield Station
The Energy Shield Test Station that was featured in the Armory Level might have also housed heavy weapons, as Sniper Rifle clips and shotgun ammo can be seen there.