At the beginning of the Vietnam war, Bell's UH1 Iroquois (nicknamed Huey due to its earlier designation of HU1) was used heavily as both medium transport and assault helicopter. The army soon realised Huey's weren't really up to the job. They were too slow to keep up with more powerful aircraft in the escort role, their body was too easy a target for ground fire and their weapons were not sophisticated enough to pick out individual targets.
What was needed was a leaner, meaner, dedicated attack helicopter, and they needed it soon.
Bell took all the dynamic parts from a Huey and put them in a body shell not much wider than a man. This provided less of a target when attacking. They added stub wings to hang rockets on, and provided a turret in the nose to which several combinations of machine gun or cannon could be attached. Ackowledging the Iroquoi's nickname of Huey, they called their new attack helicopter; AH1 Huey Cobra.