High Quality Content by WIKIPEDIA articles! The following is an extensive catalog of the variants and specific unique elements of each variant and/or design stage of the UH-1 Iroquois transport helicopter. The first Bell helicopter to use a turbine engine was a modified Model 47 (designated XH-13F), which had its initial flight in October 1954. The U.S. Army began a competition for a new helicopter for general utility and medical/casualty evacuation in 1955. In June 1955, Bell Helicopter was awarded a contract to develop the next generation turbine-powered utility helicopter for the U.S. Army. The resulting Bell Model 204 was designated XH-40 by the U.S. military and first flew on 22 October 1956. Two more prototypes were built in 1957, and six YH-40 pre-production helicopters were delivered in 1958.

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