The helicopter proved its over-battlefield value across various roles during the Korean War (1950-1953) and among those in use was the stellar Bell Model 47 (detailed elsewhere on this site), a very-light-helicopter of utilitarian makeup. The Model 47 flew for the first time on December 8th, 1945 and entered service in 1946, becoming the H-13 "Sioux" by the time of Korean Conflict and production went on to reach 5,600 units before the end with operators seen worldwide.
With this in mind, Army warplanners began to envision a future where armed helicopters ruled the battlefield and the "gunship" helicopter concept was born in which in-service types were simply modified for the attack role through various means. Before long, the dedicated "attack helicopter" concept materialized and these machines would institute definitive qualities about them to make the platforms as lethal to anything on the battlefield as possible.
By the late 1950s, Bell engineers were already working on a concept for such a helicopter and unveiled a mockup of what was designated the D-255 "Iroquois Warrior" in June of 1962 - an attacker platform built atop the existing framework and powerplant of the stellar UH-1B "Huey" transport/gunship helicopter in service since 1959. The concept involved a tandem-seat cockpit and reduced fuselage width (resulting in a most slender forward profile) with armament consisting of a single grenade launcher, 20mm automatic cannon, and support for rockets and Anti-Tank Guided Missiles (ATGMs), the latter through "wingstubs" affixed to the sides of the fuselage.
Sufficiently impressed, the Army ordered a "proof-of-concept" demonstrator from the company that December, resulting in the Model 207 "Sioux Scout" itself based upon the framework of the Bell model 47 multirole performer.
The general form of the Model 47 was retained but engineers introduced all manner of streamlining and qualities more akin to modern-day attack helicopters. The cockpit involved a tandem-seat arrangement in which the aft crewmember (pilot) sat above the forward crewman (weapons specialist), giving both operators relatively excellent vision "out-of-the-cockpit". The wingstubs were, rather interestingly, seated high along the sides of the fuselage and aft of the cockpit. These appendages were intended to mount the planned ATGMs and rocket pods (while also adding the natural effect of stabilization/improved controlling lacking in the Model 47). The primary, standard armament was an Emerson Electric TAT-101 powered turret in the "chin" position fitting 2 x M60 General Purpose Machine Guns (GPMGs). Traversal of this unit would allow some flexibility to any forward attack by offering broad firing arcs.
While on the ground, the helicopter sat on a fixed, four-point, twin-skid assembly giving a rugged quality to the machine while also simplifying maintenance and operating costs. The main rotor was positioned atop a thin mast and consisted of a simple two-bladed arrangement. The tail rotor unit was of equally-simplistic two-bladed design and faced the starboard side of the helicopter, encapsulated in a thin protective ring to shield it against ground strikes.
Power for the Model 207 became a single Lycoming TVO-435-A1A 6-cylinder air-cooled piston engine developing 260 horsepower driving both the main rotor and tail rotor blades in unison.
In its modified form, the Model 207 achieved first-flight on June 27th, 1963 and offered improved performance and handling over the original Model 47. During the remainder of its developmental phase, the structure underwent various changes to exact any and all performance from the existing airframe. The completed model was then handed over to the Army for testing before the end of the year and evaluations followed during 1964 - resulting in lessened interest in the machine on the part of the U.S. Army with shortcomings cited as lacking the required power and size for the attack requirement.
Based on this showing, however, the service evolved their needs to establish the "Advanced Aerial Fire Support System" (AAFSS) program which eventually involved Bell's newer D-262 approach (a dimensionally smaller form of the original D-255 debuted back in 1962). This was another attack helicopter concept also based in the UH-1. The project's contract was eventually claimed by the competing Lockheed AH-64 "Cheyenne" design (detailed elsewhere on this site) which, itself, failed to materialized beyond a dozen or so prototype and developmental forms, marking Lockheed's one and only foray into the helicopter market.
The Model 207, meanwhile, fell to the pages of Army aviation history as nothing more than a footnote. Bell Helicopter would eventually find success after all this work in selling the U.S. Army on its Model 209 which entered service as the AH-1 "HueyCobra" attack helicopter - keeping the important traits established by the Model 207 all those years ago: tandem-seat cockpit, skid undercarriage, twin-bladed main and tail rotors, side-mounted wingstubs, and a powered chin turret.