 Originally designated the Avro 529B, the new 320 hp (240 kW) ABC Dragonfly I nine-cylinder engine was specified, but with a redesign in July 1918, the type number was subsequently changed to Avro 533.When the original engines were not available, the 300 hp (220 kW) Siddeley Puma engine was substituted on the second prototype in November 1918, this acquiring a new designation, the Avro 533A Manchester Mk II, and first flying in December that year.An American 400 hp (300 kW) Liberty engine was also proposed as an alternate engine.