Helicarrier

"Gentlemen, you might want to step inside in a minute. It's going to get a little hard to breathe." "Is this a submarine?" "Really? They want me submerged in a pressurized metal container?"

- Natasha Romanoff, Steve Rogers, and Bruce Banner

The S.H.I.E.L.D. Helicarrier is a high-tech flying aircraft carrier, specifically designed to be itself capable of independent powered flight in addition to the conventional functions of aircraft carriers. It served as the headquarters of S.H.I.E.L.D.

History
The exact date of the Helicarrier's construction is unknown, but it was known the vessel was finished and used by S.H.I.E.L.D. in 2012. At some point after the "Big Week", the Helicarrier was docked at the secret US naval base. A spy infiltrated the ship and tried to steal Nick Fury's data about the Avengers Initiative, but he was intercepted by the S.H.I.E.L.D. agent Natasha Romanoff which was revealed to be a security exercise.

In May 2012, Fury brought Tony Stark, Bruce Banner, and Steve Rogers on board the Helicarrier, trying to form a team that could protect the Earth better than S.H.I.E.L.D. ever could. However, because of Loki's manipulations, all members of the team showed not even the slightest trace of unity and teamwork.

When the Helicarrier fell under attack from Loki's mind-controlled soldiers, it was heavily damaged, yet it was still able to limp to open water on the strength of only three of its colossal fans. When the Chitauri invaded New York City, the World Security Council ordered Fury to fire a nuclear missile at the city, but he refused. When one fighter plane tried to fly from the carrier, Fury stopped it with a rocket launcher. However, he was unable to stop the second plane which fired the missile. Thanks to Iron Man, the missile ended up shooting and destroying the Chitauri flagship, which effectively ended the invasion.

Capabilities
The Helicarrier is a seaworthy ship capable of VTOL flight by way of four huge lift fans mounted on the sides. It has two runways, one with direct access to a hangar at the rear is aligned along the spine of the vessel and is used for forward launches of aircraft, and the other diagonally aligned runway above is suitable for landings.

Trivia

 * In the comics, the helicarrier was more of a glass dome. Joss Whedon felt it would be more realistic if it was more like an aircraft carrier.