In February 1942, Chadwick submitted his drawings to Avro's experimental department. Within five months, the company refined the design and had quickly assembled an initial prototype. On 5 July 1942, the York prototype, "LV626", conducted its maiden flight from Ringway Airport, Manchester. It had initially been fitted with the twin fins and rudders of the Lancaster but the increased fuselage side area forward of the wing compared to the Lancaster necessitated fitting a third central fin to retain adequate control and directional stability; the third fin was fitted as standard on subsequent production aircraft. Flight trials of "LV626" were quickly transferred to RAF Boscombe Down. In response to the prototype's favourable performance during trials, the Air Ministry issued an order for three more prototypes of various configurations to be built along with an initial production batch under Specification C.1/42, part of Operational Requirement OR.113 for a new transport aircraft.