The S.6B was last in a line of racing seaplanes to be developed by Supermarine, followed on from the S.4, S.5 and the S.6. Despite these predecessors having twice won the Schneider Trophy previously, the development of the S.6B was troubled by wavering government support, being promised, withdrawn, and then issued once again following a high-profile public campaign encouraged by Lord Rothermere and a substantial donation by Lady Houston. Once government backing had been secured, there were only nine months remaining until the race, thus Mitchell decided to refine the existing S.6 rather than pursue a clean-sheet design, thus the type's designation of "S.6B".