Like the Avro Manchester, the Handley Page H.P.53 Hereford was basically a good airframe with a bad engine. The H.P.53 prototype, converted from the prototype of a Swedish patrol version of the Hampden, was flown in June 1937 with two 955 h.p. (712 kW) Napier Dagger VIII H-type engines, and Short Brothers and Harland was contracted to build an initial batch of 100 aircraft, a number later increased to 152. The first of these production aircraft from the Belfast line flew on 17th May 1939.
Tests at the Aircraft and Armament Experimental Establishment, Martlesham Heath, showed the Hereford's performance to be almost the same as that of the Hampden, but there the similarity ended. The engines were unreliable, over-heating on the ground and cooling too rapidly when airborne, while the very high pitched exhaust note proved uncomfortable for the crews.
One or two Herefords served alongside Hampdens in operational squadrons for a very short time, but were soon relegated to a training role, primarily with No. 16 Operational Training Unit (OTU) at Upper Heyford, Oxon, where first deliveries were made on 7th May 1940. Another Hereford unit was No. 14 OTU at Cottesmore, which had begun to operate the type as No. 185 Squadron; it was retitled No. 14 OTU in April 1940. One Hereford was used by the Torpedo Development Unit at Gosport, and at least 19 were subsequently re-engined and converted to Hampden standard.