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 organizations such as Hydra with domestic political fallout sure to follow immediately thereafter.
The main S.H.I.E.L.D. Helicarrier is 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. 
Constructed in secret there are at least nine Helicarriers have been built over the decades, and at least two have been in simultaneous service in the last decade on several occasions. Also, at least seven Helicarriers have been named over the years:
- Luxor (not yet seen - a class prototype)
- Behemoth (smaller version used by S.H.I.E.L.D.'s Godzilla Squad)
- Hermes (allegedly scuttled after being hijacked by the Red Skull)
- Argus (a Luxor-class Helicarrier)
- Black Hawk (destroyed in action against the Hydra-Hand alliance)
- Pericles V (infiltrated by the vampiric Order of Tyrana and scuttled by Blade)
- Iliad (currently in use)
It is not yet known what criteria S.H.I.E.L.D. has used to name the Helicarriers.
Ultimate Universe (Earth-1610)
The Ultimate version of S.H.I.E.L.D. had a fleet of airborne aircraft carriers (prior to the assault by the Liberators), one of which was referred to, at one point, as the Helicarrier. They aren't S.H.I.E.L.D. primary HQ, this being the Triskelion. The engines that keep the carriers aloft were designed by Tony Stark and were modular enough to be used in a space shuttle by the Ultimate Fantastic Four. These fleets of Helicarriers are smaller than the Earth-616 Helicarriers and are more conventional aircraft carrier shape, but are far more plentiful.
One Helicarrier, the U.S.S. Jimmy Carter, was used as the command center for the New Ultimates briefly while they were under the direction ofGregory Stark. Gregory Stark also noted that this realities Hank Pym was the orginal designer of the Helicarrier, although it has been enhanced and upgraded with Stark technology. 
Insane Impossible Man (Earth-14845)
On Earth-14845, The Impossible Man has the ability to shape-shift anything he wants to at will. When The Controller slaps a Slave Disc on him, The Impossible Man goes crazy, and crashes the S.H.I.E.L.D. Helicarrier before transporting all of the agents along with the rest of the people in Washington, D.C. to "Mouse-Land" in California.
Bullet Points (Earth-70105)
Marvel Noir (Earth-90214)
The Army Air Force built a "Dirigi-Carrier", a airborne battleship kept in midair by dirigibles right underneath the vessel. The Dirigi-Carrier was used as the base of the Office of National Emergency (O*N*E*).
The Avengers: Earth's Mightiest Heroes (Earth-8096)
S.H.I.E.L.D. utilizes this Helicarrier in this animated series as it's main HQ and military command airship.
It was destroyed during the Skrull Invasion.
House of M (Earth-58163)
The Helicarriers of the House of M Universe were owned and operated by Magnus' House of M.
Marvel Cinematic Universe (Earth-199999)
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. The Helicarrier was heavily damaged in an attack, yet was still able to limp to open water on the strength of only three of its colossal fans.
Ultimate Spider-Man (Earth-TRN123)
The Helicarrier serves as the mobile airborne headquarters of S.H.I.E.L.D.. That is, until its destruction at the hands of the Green Goblin. It's later replaced by the larger and more versatile Tri-Carrier.
- The British organization W.H.O. utilized a Helicarrier of their own.
- According to intel gathered by project Livewire, five Helicarriers are known to have been wrecked, two off the coast of NYC, though several more are known to have been lost since then.
- One of the crashed helicarriers was re-built by an illegal black ops project and subsequently destroyed by the Livewires.
- No trivia.
- S.H.I.E.L.D. Helicarrier's Comic Appearances
- Vehicle Gallery: S.H.I.E.L.D. Helicarrier
- Images that include S.H.I.E.L.D. Helicarrier
Links and References