In March 1965, Bell began developing an attack helicopter for close air support based on the Model 204 (UH-1B/-1C Iroquois). The plan was to provide the U.S. Army with a test helicopter that would combine a new narrow fuselage with a small cross-section and a tandem seating arrangement, along with the engine, main rotor, and transmission of the UH-1C helicopter. The helicopter, designated Model 209, was tested starting in December of the same year. In April 1966, orders were placed for two pre-production models and 110 production units.

The helicopter, ultimately designated AH-1G and referred to as the Huey Cobra, was delivered to the U.S. Army starting in June 1967 and saw combat operations in Vietnam by September. A total of 1,127 AH-1Gs were delivered to the U.S. Army, including the TH-1G dual-control training helicopters.

The production helicopter AH-1G, which served as the basis for further modifications, featured a single-rotor design with a tail rotor, a gas turbine engine, and a ski landing gear. The fuselage was entirely metal and semi-monocoque. The cockpit was two-seat, with the gunner's and pilot's seats arranged in tandem. The floor in the gunner's area (in front of the pilot) was 0.25 m lower. The canopy with flat glass minimized glare and increased the space above the pilot's head. The helicopter was equipped with an advanced autonomous system for jettisoning emergency windows and doors. Light steel armor protected the crew and the most critical areas of the structure and components from ground fire. The structure of the tailboom was reinforced to withstand 23-mm projectiles. The helicopter's airframe was painted to reduce its visual and infrared signature.