Triskelion (Ultimate Avengers)

The S.H.I.E.L.D Headquarters is the main base of S.H.I.E.L.D. (Strategic Homeland Intervention Enforcement and Logistics Division) second to the Helicarrier.

History
Its history was largely unknown after S.H.I.E.L.D.'s formation.

Its location is in New York Harbor where the Helicarrier and other military aircraft are docked and military weapons and equipment are stocked there.

This headquarters possessed the best computer and security system designed by Tony Stark. It has a lot of rooms inside the HQ: the War Room, the Communications Room, the Rebirth Chamber, the Briefing Room,labs,medical facilities,and armories,etc.

The SHIELD HQ is quite known for being vulnerable for a Chitauri attack when they invaded Earth with a couple of Chitauri warships and a handful of Chitauri units.All SHIELD units did their best to stop them including the Helicarrier but they couldn't stop them due their opponents' vibranium armor. But the Avengers had stopped them aided by Nick Fury and Hulk who was overcome with rage forcing the team to fight him after the battle with the Chitauri invaders.

After the first Chitauri attack, the SHIELD HQ was later rebuilt with new structural changes and new defensive systems provided by Stark Enterprises.

When the second Chitauri invasion begins, every part of the globe is under attack. All militaries including SHIELD had tried to fend off the attack but were greatly outgunned and outnumbered. Even the SHIELD HQ was under attack again as Chitauri troops entered it. But once again the Avengers saved the world again assisted by Black Panther, Nick Fury, and Hulk who later went into hiding after the battle.

The SHIELD Headquarters was later rebuilt.