The Hydra is the GTA San Andreas equivalent of the Harrier Jump Jet, and the first fighter plane to appear in any GTA game. It is a very fast and agile aircraft, and it can shoot unlimited heat-seeking missles, and also release flares as missile countermeasures. It is available from the aircraft carrier in the Easter Basin Naval Station, from Area 69 in the desert, the nearby Verdant Meadows airstrip and on Sweet's house roof (when the game is completed 100%). The hydra is the only vehicle that does not require a third party program to access that can reach the maximum height. The hydra is a great plane but is sometimes hard to fly.
The Hydra is a Vertical Take-Off and Landing (VTOL) craft. When entered, it is on hover mode by default. When in this mode, it controls like a helicopter, though is somewhat harder to control. Once jet mode is enabled, it can control like a jet, and can go at very fast speeds. It can also be turned back into hover mode, either to land, or to offer a more stable gunplatform for shooting as ground targets or helicopters.
If a player is dogfighting with other Hydra's, the player will almost always win, as the enemy craft are not only usually worse pilots, they also do not take evasive maneuvers or launch countermeasures when a homed missile is fired at them.