During July 1937, Handley Page was instructed to redesign the HP56 to use a four-engine arrangement, instead of the original twin-engine configuration; by this point, the Vulture had already been suffering from reliability and performance problems. The rival Avro 679 proceeded into service as the Avro Manchester powered by a pair of Vulture engines, but was only built in limited quantities after suffering substantially from engine-related difficulties. The four-engine redesign increased its wingspan from to and added of weight. In September 1937, the Ministry specified the use of four Rolls-Royce Merlin engines; according to aviation author Phillip J. R. Moyes, this redesign to four Merlin engines had been done "much against the company's wishes".