The Helicarrier, an aircraft carrier specifically designed to be itself capable of independent powered flight in addition to the standard functions of aircraft carriers, is the world headquarters and signature capital ship of the extra-governmental intelligence/defense agency S.H.I.E.L.D..
Built by Stark Industries and designed by Tony Stark, Dr. Reed Richards, and former X-Man Forge. In addition to housing wings of fighters and other aircraft, the Helicarrier bristles with advanced weaponry, including an intercontinental ballistic missile.
The first Helicarrier was proposed by Stark Industries as a political compromise among the signatories of the treaty in response to fears that any nation hosting the Directorate's main headquarters would be subject to attack by hostile organizations such as Hydra with domestic political fallout sure to follow immediately thereafter.
When Tony Stark himself became Director of S.H.I.E.L.D., he ordered construction of a red-and-gold Helicarrier in the motif of his Iron Man Armor. This Helicarrier was brought down by the Red Hulk to be rebuilt as the Hellcarrier, the headquarters of the Intelligencia.
The main S.H.I.E.L.D. Helicarrier was disabled by an alien computer virus unleashed by a Skrull agent posing as Edwin Jarvis as part of the Secret Invasion. When the Skrull Invasion was over and Norman Osborn the new director of S.H.I.E.L.D. (now called H.A.M.M.E.R), he soon ordered to dismantle it, to build his own H.A.M.M.E.R. Hellicarrier.
After the Siege of Asgard, Steve Rogers became world's new Top Cop, deposing Norman Osborn and dismantling H.A.M.M.E.R., but without reinstalling S.H.I.E.L.D.
After the attack of the Serpent and the return of H.A.M.M.E.R., Rogers decided to reactivate S.H.I.E.L.D. and build a new Helicarrier called Iliad. Iliad remains a primary vessel for Daisy Johnson, Maria Hill, and the current team of Secret Avengers.
The current Helicarrier (similar to its previous model, Iliad) is stationed above New York City; this model can traverse the sea as well as in the sky. As well as it is built for combat, this model can also house a superhero team, complete a meeting room exclusive to the team, as well as their own living quarters.