As work continued on the SR.53, a separate High Speed Development Section was formed by Saunders-Roe to work on the SR.177. Initially, the SR.177 was a straightforward development of the SR.53, sharing much of the same configuration and equipment, and it was envisioned that the first test flight would take place during the first half of 1957. However, in February 1955, an extensive redesign of the SR.177, with the aim of making the type suitable for use by both the RAF and the Royal Navy, was commenced. Of the changes made to the aircraft, major differences included the repositioning of the jet engine to the lower fuselage lobe, which was now fed with air via a large, chin-mounted intake; the wing was also enlarged and blown flaps were adopted. The turbojet engine selected was the de Havilland Gyron Junior, capable of generating of thrust.