Cobra Island is a fictional country located in the Gulf of Mexico. It is the main base of operations for the fictional Cobra Organization featured in the G.I. Joe toyline from the 1980s. It is featured in the G.I. Joe cartoon and the comic book series created by Marvel Comics and Devil's Due Publishing. It is also a fictional island in the Caribbean in the Burt Lancaster film The Crimson Pirate, made in 1957.
In the comics, Cobra Island is in the Gulf of Mexico. The island is artificially created as the result of a plan by Crimson Guard scientist Professor Appel. False information in Appel's home led the Joes to target an underwater bunker with a massive drop of non-nuclear bombs. The explosion triggered a faultline releasing volcanic stresses forcing an area of the ocean floor containing a sunken freighter Cobra base to rise above sea level.
Realizing the strategic value of the new territory, G.I. Joe attempts to dislodge Cobra from the island via a pitched assault. The G.I. Joe team had nearly won when they were called off by the United States, as lawyers in Cobra's employ had successfully maneuvered to get the island sovereign nation status and recognition by the U.N.
Many important facilities are established on the island, such as the Terror Drome fortress, a dedicated surgical hospital, an airfield and luxury hotel for visiting dignitaries (usually third-world dictators looking to buy weapons). One of the main features is the now "land-locked freighter", a seemingly mundane sunken cargo ship raised up with the island which hides a storehouse of advanced technology (including the Cobra space shuttle and launch facility) and is frequently used as an operations center. After Cobra is forced to retreat from Springfield  the island gains a significant civilian population.
Geographically the island is very small, barely 5 square miles (10 km2) in area. Its most prominent feature is its central active volcanic peak, created by the same forces which originally raised the island. The G.I. Joe team mountaineering expert Alpine commented that the volcano is unusually rough, jagged and steep, whereas most volcanic mountains are characterized by smooth regular slopes. Other terrains include tropical jungle (which grew quickly on the new island) and a swamp in which Croc Master maintained security with his trained crocodiles.
As an actual nation, it was forbidden for the G.I. Joe team to violate its airspace or territory, though of course Cobra had no qualms about spying on U.S. soil.
Some time later, Cobra Island is threatened by an advanced missile controlled by a rogue faction in the United States military. The threat results in a battle between unofficial Joe forces, General Hawk himself and the mercenary Dreadnoks. A Cobra transport helicopter, sent from the Consulate in New York City destroys the weapon.
Cobra Civil War
The largest conflict to occur on the island was the Cobra Civil War. Tensions between Serpentor and the Crimson Guardsman Fred VII (masquerading as Cobra Commander) caused by competition for control of Cobra exploded into open combat between the different factions. The fighting would grow to involve G.I. Joe and Destro's Iron Grenadiers as well, with the Joes ordered to side with Serpentor's constitutional monarchy and Destro remaining neutral to either faction. Control of the airfield became a major turning point in the short war. Serpentor's faction was on the verge of seizing victory when he was assassinated by Zartan, leaving Fred VII unopposed, while Destro was permitted to leave with his prize, the Baroness.
The true Cobra Commander later returns and reclaims his position. He uses the land-locked freighter as a prison for many who opposed him, such as Doctor Mindbender and Raptor. He causes a mountain-damaging lava flow that buries the freighter. Most of the prisoners perish; Firefly, Zartan and Cobra Commander's son Billy manage to escape, while Doctor Mindbender is revived years later by Cobra Commander.
After the Trucial Abysmia war with G.I. Joe, Cobra Island is largely abandoned as Cobra Commander takes the organization's operations around the world. Some operatives, such as Zarana and Cesspool, are stationed there, and are present when Firefly and his personal army of Battle Android Troopers take over, but the island is deserted again after a confrontation with the Joes.
It later serves as the base of operations for a revived Serpentor and his personal army called The Coil. Over the years, the geography has greatly changed. While in the past it had been a relatively flat island with one mountain, now it had towering cliffs surrounding a fortified harbor.
After the defeat of Serpentor, the U.S. Government sells Cobra Island to what seems to be a research firm called "Gen-Tek". As discovered by a Joe assault force, this company is yet another Cobra front. The purchasing was handled by the Cobra businessmen Tomax and Xamot. It serves as Cobra's headquarters before the organization moved to the Monolith Base. Remnants of The Coil, abandoned on the island following the defeat of Serpentor, are present when the island was destroyed after the G.I. Joe team drops a nuclear weapon on it. 
In the alternate universe of G.I. Joe Vs. Transformers 2, Cobra Island is a natural island in the Caribbean. It is the site of a showdown between Cobra, G.I. Joe, Autobots and the Decepticons.
In the Sunbow G.I. Joe cartoon, Cobra Island's location and origins were never explained. It debuted in the first season two-parter "There's No Place Like Springfield" as the secret location of Cobra's main headquarters. The island served as the home of the Terror Drome throughout season two.
The Terror Drome is largely destroyed during the events of G.I. Joe: The Movie. After Sgt. Slaughter, Lt. Falcon and the Marauders successfully infiltrate the Terror Drome to spy on Cobra's activities, they rig the complex to explode and make a hasty (yet combative) departure.
Cobra Island is a featured location in the G.I. Joe novel 'Fool's Gold'.
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