In 1962 the US Army initiated its' Army's Advanced Aerial Fire Support System (AAFSS) program which had a tank-killing capability as a high priority. Bell responded by offering a version of the UH-1 Iroquois as the Design D-255 Iroquois Warrior. As a private venture Bell also produced the Model 207 Sioux Scout as a concept evaluation vehicle, first flown in July 1963 it was well received by the US Army, but a larger turbine-powered aircraft was preferred. Bell scaled down their D-255 as the Design D-262 which was tendered for the AAFSS contract in the 1964 competition. The Lockheed AH-56A Cheyenne and the Sikorsky S-66 were selected for the final evaluation process.
Charlie Siebel, chief experimental helicopter projects engineer at Bell, believed that the Army would soon be looking for an interim capability while the highly complex and costly AAFSS aircraft went through the development phases. He got approval to develop the Model 209, based on the UH-1 dynamic system, but with an 8ft (2.44 m) wide tandem-cockpit fuselage and an extensive array of ordnance systems. Army announced that they were seeking an interim gunship for operations in South East Asia and Bell formally offered the Model 209, and the AH-1 HueyCobra was first flown on September 7, 1965. Bell won a fly off against the Kaman UH-2 Seasprite and the Sikorsky S-61 and a development contract was signed in April 1966. The AH-1 HueyCobra became the first attack helicopter to go in series-production and entered operational service in 1967.
With the reduction of the activities in the Vietnam War in 1969 the US Army's focus turned to operations in Europe against Warsaw Pact forces and an attack helicopter with a tank-killing capability was re-emphasized as a high priority. Bell considered that an AH-1 HueyCobra with TOW (tube-launched optical-tracked wire-guided) anti-tank missiles could fill the gap and produced the Model 309 KingCobra as a private venture. The first aircraft (N309J) flew on September 10, 1971 powered by a Pratt & Whitney Twin Pac turbine engine and intended as an replacement for the USMC AH-1J SeaCobra. The second flew with a Lycoming T-55 turbine engine for the first time on January 31, 1972 and was to be offered to the US Army.
However the second prototype suffered from an accident in April 1972, so to participate in an Army evaluation of potential gun ships, the first prototype had its Twin Pac engine replaced by the Lycoming engine to suit the Army requirements. One other evaluated helicopter was the Sikorsky S-67 Blackhawk but neither of these types were ordered.
In November 1972 the US Army issued a request for proposals for their Advanced Attack Helicopter developing program to which Bell responded with the Model 409, resulting in June 1973 in a contract for two prototypes and a ground test vehicle. The two KingCobras have been used as research vehicles for this and other programs.
The KingCobra had the general configuration of the HueyCobra but had the wing stubs enlarged to a span of 13 ft (3.96 m), 5 ft (1.52 m) enlarged new designed rotor, 4 ft 7 in (1.40 m) longer fuselage and a tailboom extension. The General Electric chin barbette could mount a 0.79 in (20 mm) or 1.18 in (30 mm) rotary cannon, the wings had four hard points for various weapons like up to eight Hughes TOW missiles and two 19-tube rocket pods with 2.75 in (70 mm) FFARs (folding-fin aircraft rockets). The multi-sensor fire control system comprised infra-red, laser and low-light-level television systems.