The early 1930s were times of worldwide economic depression and as the date for the 1931 Schneider Trophy approached it seemed highly unlikely that the government would provide money for any new aircraft. Mitchell was frustrated. Like the Italians and Americans before, Britain was now in a position to win the Schneider Trophy outright, with three consecutive wins, but Supermarine were not able to fund the development of a new plane and, despite declarations of intention to compete from both France and Italy at the end of 1930, the government announced in January 1931 that expenditure of public money to support the contest was not justified.
Despite efforts to encourage the government to change its mind by highlighting the steadily rising export trade in British aircraft, largely due to the attention that the Schneider competitions had generated, Mitchell gave up all hope of there being a 1931 contest. Then, quite out of the blue, the situation was saved by Lady Lucy Houston, the widow of a millionaire ship owner, who made an unsolicited gift of £100,000.
By now the 1931 Schneider Trophy was only seven months away and in that time Mitchell could not hope to produce an entirely new S.7. Instead, he decided to concentrate on making some changes to the S.6 design, with the primary aim of accommodating the more powerful version of the Roll-Royce "R" engine that raised the power output of the 1929 version from 1,900hp to 2,350hp. The major problem was to allow for the dissipation of the extra heat produced by the more powerful engine; a total of 40,000 BTUs of heat had to be got rid of. All major changes were directed to this requirement with the floats being lengthened to provide more cooling area, whilst further modifications were made to the intricate oil cooling system. Even then it was necessary to fly the S.6B according to water temperature rather than simply at full throttle. Mitchell often referred to his S.6B as essentially a flying radiator!
Two new S.6B seaplanes were built and given the military serial numbers S.1595 and S.1596. The two 1929 S.6s, N247 and N248, were modified to take the new S.6B floats and the new engines. As such, they were designated S.6As and would be available as reserves for the race.
A new RAF High Speed Flight was formed, again under the command of Sqd Ldr Orlebar. The pilots eventually selected were Flt Lt JN Boothman, Flt Lt GH Stainforth, Flt Lt FW Long, Flt Lt EJL Hope and Flg Off LS Snaith, later to be joined by Lt RL "Jerry" Brinton from the Fleet Air Arm. They arrived at Calshot in May.
The first aircraft to arrive was one of the modified S.6s (N247), and Orlebar took it up for the first time in June. It developed an alarming rudder flutter at speed and everyone, not least Mitchell, was relieved when Orlebar brought it down safely. As a result of this experience, mass balances were fitted to the rudder, elevator and ailerons, not only to N247 but also to the second S.6A (N248) and to the two S.6Bs under construction.
Later in June, when it finally became available with its upgraded engine, N248 experienced an engine splutter which forced Orlebar to land. On inspection it was found that the fuel filter had become clogged. Even when thoroughly cleaned the same thing happened again. It was discovered that the problem was due to a certain component in the new fuel taking away the surplus compound which sealed the tanks and the new "Superflexit" pipes. Boothman later recalled that Mitchell's answer was short and to the point. "You will just bloody well have to fly them until all that stuff comes off!" which they did, and it worked. Again Mitchell's urge to try the simple solution was proved right.
At last, on 21 July, the first S.6B (S.1595) arrived at Calshot. Its maiden flight, piloted by Orlebar, caused many anxious moments as he was unable to get it off the water. The plane would swing violently through 120 degrees and Orlebar later likened it to a kitten chasing its tail. Mitchell knew this was caused, again, by the extra torque of the engine, over which he had no control.
After careful calculations and tests, including fitting the smaller diameter S.6B propeller on to N247 where exactly the same problems occurred, he determined that a larger propeller of 9ft 11/2in diameter was required.
The 1931 Schneider Trophy was planned to take place on 12th September. All hopes of an exciting race began to fade when France withdrew her entry and then, in August, following the death of their top pilot, Monti, Italy also pulled out. On September 3rd, both France and Italy requested a postponement of the race but, unlike the Americans in 1924, the British Royal Aero Club refused.
It was feared that there would be little interest in the race without any foreign challengers, however plans went ahead. It was decided that Boothman in S.1595 would try to win the Trophy with Snaith and Long as first and second reserves, in N248 and S.1596 respectively. Later, Stainforth would attempt to establish a new world air speed record.
The morning of the race started fine but later it began to rain, and with strong winds whipping up the sea, the race was postponed. Fortunately the next day the wind dropped and once again huge crowds gathered, with Southsea one of the most popular vantage points.
Boothman lapped the 50km triangular course seven times at an average speed of 340.08mph, nearly six miles a minute, and successfully won the Schneider Trophy outright.
At 4pm on the same afternoon, Stainforth went up in S.1596 and set a new world speed record of 379.05mph. Later, on 29th September, Stainforth smashed his own record, by nearly 20mph, with a speed of 407.5mph.
Sqd Ldr Orlebar, who had shared with his friend Mitchell both triumph and disasters, later wrote in his book, Schneider Trophy, "The credit belongs to the brains which conceive, not to the hands which hold. But the hands had very good fun."
The last contest was over and, thanks to Mitchell, Supermarine, Rolls-Royce and the pilots of the RAF High Speed Flight, the trophy would remain in Britain in perpetuity.