Following a Tender Design Conference in October 1936, the S.29 was low down on the short list of designs considered. Vickers Type 293 submission was first followed by the Boulton Paul P.90, Armstrong Whitworth's AW.42, the Supermarine Type 316, and then the Short S.29. The Supermarine was ordered in prototype (two aircraft) form as the revised Supermarine Type 317 in January 1937. An alternative design to the Supermarine was needed for insurance and Shorts should build it as they had experience with four-engined aircraft. The original design had been criticized when considered and in February 1937 the Air Ministry suggested modifications to the design, including considering the use of the Bristol Hercules radial engine as an alternative to the Napier Dagger inline, increasing service ceiling to 28,000 ft (carrying a 2000 lb of bombs) and reducing the wingspan. Shorts accepted this large amount of redesign work. The project had added importance due to the death of Supermarine's designer, Reginald Mitchell, which had generated doubt within the Air Ministry about the ability of Supermarine to deliver. Two prototypes were ordered from Shorts.