Short Sunderland - Development

Development

The early 1930s saw intense competition in developing long-range intercontinental passenger service between the United Kingdom, the United States, France and Germany, but the United Kingdom had no equivalent to the new American Sikorsky S-42 flying boats or the German Dornier Do X. However, in 1934, the British Postmaster General declared that all first-class Royal Mail sent overseas was to travel by air, establishing a subsidy for the development of intercontinental air transport in a fashion similar to the U.S. domestic program a decade earlier. In response, Imperial Airways announced a competition to design and produce 28 flying boats, each weighing 18 tons (18.2 tonnes) and having a range of 700 mi (1,100 km) with a capacity for 24 passengers.

The contract went to Short Brothers of Rochester and while the first example of the new type, the S.23 Empire was under development, the British Air Ministry was taking actions that would result in a military version. The 1933 Air Ministry Specification R.2/33 called for a next-generation flying boat for ocean reconnaissance. The new aircraft had to have four engines but could be either a monoplane or biplane design.

Specification R.2/33 was released roughly in parallel with the Imperial Airways requirement, and while Short continued to develop the S.23, it also worked on a response to R.2/33 at a lower priority. Chief Designer Arthur Gouge originally intended that a 37 mm COW gun be mounted in the bow with a single Lewis gun in the tail. As with the S.23, he tried to make the drag as low as possible, while the nose was much longer than that of the S.23. The military flying boat variant was designated S.25 and the design was submitted to the Air Ministry in 1934. Saunders-Roe also designed a flying boat, the Saro A.33, in response to the R.2/33 competition, and prototypes of both the S.25 and A.33 were ordered by the Ministry for evaluation. The initial S.25 prototype first took flight in October 1937.