It has often been said that the Lancaster arose from the failure of the Manchester. This is not entirely true; as early as the autumn of 1938, long before the first flight of the Manchester prototype, A. V. Roe's design office considered the possibility of a four-engined variant of the Type 679. But with other priorities in the design offices, only the most basic work was done at this stage on what was to become the Avro Type 683. As a safeguard against a shortage of Merlins, the Mk 11 Lancaster was powered by Bristol Hercules radial engines. Only 300 were built. The first four-engined bomber to enter service with Bomber Command was the Short Stirling. It was inferior to the Lancaster in both performance and load-carrying.