- Jump up onto the giant metal AC duct and the skull is at the very end of it

Follow this guide to find the hidden skull located at the end of a giant metal AC duct in Halo: Reach. Learn the best strategies to clear the hanger and barracks.

Walkthrough:

1. Head down the stairs and follow the marines. Miranda will inform you that a hanger has been infiltrated and needs to be cleared.
2. Continue down the hallways to reach the hanger. Use the Right Bumper to open any hatch with a glowing green light.
3. Run past the destroyed Warthog and fight through the gauntlet.
4. Secure a Plasma Pistol and pair it with a Battle Rifle for an easier time against Jackals and Brutes.
5. Once the hallway is clear of enemies, do not go through the green lit door. Instead, run to the end of the hallway to find an Easter egg featuring the Red vs Blue characters.
6. In the Hanger, initially there is light resistance. Eventually, waves of Covenant drop ships will arrive, deploy troops, and depart.
7. Run to one of the emplaced turrets and detach it by pressing B. You will move slowly but the turret's large ammo capacity compensates.
8. Avoid shooting the energy gun turrets on the front of Covenant drop ships; save your bullets for the Brutes.
9. Utilize the red light tunnels for cover. Pop out to flank enemies and shoot them in the back.
10. After clearing the hanger, the Pelican will land and your allies will board. Master Chief must backtrack to the Op Center.
11. Before backtracking, look out of the hanger to see the gigantic Covenant ship laying siege to the city, identified as the command ship of the Profit Truth.
12. Backtrack to the ops station. On the way, enemies will breach the base, and Keys will intercom that the barracks are under attack.
13. A soldier will be attacked by a Drone.
14. Stay in the room with the cage and snipe the Drones with your Battle Rifle. Retreat to another room if your shields are low until they recharge.
15. Back in the ops center, Miranda will appear on the big screen. Troops are preparing a bomb to blow up the base after evacuation. Johnson prioritizes saving the barracks troops.
16. EASTER EGG: On the second story of the Op Center, find laptops displaying the Blue-Screen-of-Death from Halo 2's New Mombassa map.
17. The garage leading to the barracks presents the first challenging battle with Brutes in an offensive line. Rushing will result in close-quarters combat with the first line and snipers in the back.
18. Weapons: Shotgun | Battle Rifle
19. First, acquire the shotgun. Run to the end of the truck, pick up the grav lift, deploy it, and use it to reach the catwalks above. Shotguns are located in ancillary rooms on both sides of the upper deck.
20. A shotgun blast combined with a melee attack can eliminate a ground-level Brute in one hit.
21. To effectively engage the Brute platoon, hug a wall, wait for them to pass, and then shoot/melee them from the side.
22. Stay in an ancillary room to eliminate the first two Brutes, then descend to the bottom level.
23. Let the remaining Brutes approach you.
24. Shooting down the length of the hallway will result in immediate enemy fire and likely death.
25. Hide in the smaller side rooms and adopt a hunkered-down position.
26. Use the radar to track approaching enemies.
27. Be patient; enemies will seek you out. Hide in the shadows.
28. Enemies are not overly aggressive, allowing time to reload and recharge shields.
29. Prioritize eliminating the low-level Brutes first, then target the gold and chieftain Brutes.
30. Use sticky grenades for the gold Brute.
31. Once low-level Brutes are dead, the Chieftain with the hammer will attack. Maintain a distance of approximately 10 meters. Use the shotgun for close encounters to stun him, then switch to ranged weapons like a Brute Shot or Battle Rifle for sniping.
32. After defeating the Chieftain, collect his energy hammer.
33. Diversion: Place a grav lift under the semi-truck to make it float.
34. Proceed through the open door at the end of the hall.
35. Head for the small manhole. A Drone will emerge, which is a scare tactic.
36. Jump down the manhole. Cortana will appear, indicating the