In mid 1936 Specification B.12/36 was sent out to Supermarine, Boulton Paul, Handley Page and Armstrong Whitworth. In August the Specification was issued to the rest of British industry. Left out of those asked to tender designs, Shorts were later included because the company already had similar designs in hand while possessing ample design staff and production facilities to fulfil production commitments. Shorts were producing several four-engined flying boat designs of the required size and created their "S.29" proposal by removing the lower deck and boat hull of the S.25 Sunderland. The new S.29 design was similar to the Sunderland: the wings and controls were the same, construction was identical and it even retained the slight upward bend at the rear of the fuselage, which had originally been intended to keep the Sunderland's tail clear of sea spray. As originally designed, the S.29 was considered to be capable of favourable high-altitude performance.