The prototype Tudor (G-AGPF) first flew at Ringway on 14 June 1945 and testing of it and the second and third prototypes revealed some aerodynamic problems which needed some design changes, these taking some two years.

In 1941 Chief Designer for Avro, Roy Chadwick, commenced preparing drawings for a long- range transport aircraft based on the Avro Lancaster, culminating in the Avro 685 York. The prototype (KV626) flew for the first time on 5 July 1942.