With the Miles M.60 Marathon, the company broke new ground, for it was the company's first all-metal aircraft and the first with four engines. Flown in 1946 with Gipsy Queen 71 engines, the Marathon was the winner in a competitive bid to Air Ministry Specification 18/44, and the Ministry ordered three prototypes for BOAC.
Miles was frustrated severely by the vacillations of the Ministry of Aircraft Production, which gave orders and counter orders throughout the pre-production stages, but when the prototype flew, test pilots soon found it was a very pleasant aircraft to handle. Loss of the prototype in a fatal crash during trials at Boscombe Down was attributed to pilot error. The second prototype flew in February 1947, but before a production contract could be signed the Miles company suffered financial collapse and its aircraft assets were eventually acquired by Handley Page.
The company became Handley Page (Reading) Ltd. and the M.60 Marathon was redesignated Handley Page H.P.R.1 Marathon I. A production order for 50 was placed, 30 for BEA and 20 for BOAC's associated companies. In the event the BEA order was reduced to 25 and later seven, then cancelled completely, and 28 of the Marathons were modified for use by the RAF as navigation trainers as the Marathon T.Mk.11, serving for six years before being replaced by Vickers Varsities. Handley Page built only 40. The remaining aircraft operated in a number of overseas countries including West Germany, Jordan, Nigeria, Canada, Japan and Burma. Some were used experimentally, including use as engine test-beds, and the last survivors were scrapped around the mid-1960s.
The M.69 Marathon II was the designation of single prototype, flown by the Handley Page company, initially with two 1,010 hp Armstrong Siddeley Mamba turboprop engines; later used to test two Alvis Leonides Major radial engines.