Cooling the engines required radiators on every available surface on the plane — wings, fuselage, the front of the floats and even the struts that supported the floats. The oil tank was in the lower front cowling, and two pumps circulated the oil in two stages. Four oil coolers with filters were placed on the rear of the floats. Fuel was housed within the floats and was independently drawn to each engine, which generated power for both of the fuel pumps. The cooling system was complex and expensive, but it worked.

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The Macchi racer’s structure was of steel tubing covered with sheet duralumin forward of the wings, and wood with plywood covering aft, including the tail surfaces. Plywood was used for the lower part of the floats and duralumin for the upper part.

Castoldi’s new contender was designated the Macchi-Castoldi M.C.72 in his honor, and five were to be produced. Three were completed in 1931, but the development program suffered a tragic setback when the first one, after reaching a speed of 375 mph, crashed, killing Giovanni Monti. The Italians petitioned for the race to be postponed, but Britain refused, effectively eliminating Italy and France — whose entry was not ready, either — from participating in the 1931 race.

Meanwhile, Reginald Mitchell had refined his S.6 further to use a new version of the Rolls-Royce R, which could generate 2,350 hp without a significant gain in weight over the 1929 model. But at first it looked as if Supermarine would not have his S.6B ready either, for the firm was low on funds, and the Air Ministry refused to spend any more money on a racing event. At that point, however, Lady Lucy Houston intervened, contributing 100,000 pounds sterling to ensure that Britain did not win the race merely by default — and to give herself a forum to castigate Britain’s Labor government. Even Mussolini himself could scarcely have surpassed Lady Houston’s rhetoric. Every true Briton would rather sell his last shirt than admit that England could not afford to defend herself, she declared.

Originally scheduled for the second Saturday in September, the 1931 Schneider Trophy race was held up for one day due to bad weather, but the following day, September 13, turned out sunny and clear. The two contestants, both Supermarine S.6Bs, prepared to take off from Lee-on-Solent to begin the 217.48-mile course before an audience of nearly a million, crowding the coast of Portsmouth and the Isle of Wight. As his blue and silver S.6B, S1595, was pushed off its barge near Calshot Castle, Flight Lt. John N. Boothman speculated on whether he would complete the triangular 33-mile laps seven times as planned. Even with five long fluted radiators down each side of its fuselage, he feared that his plane would be unlikely to last more than 90 minutes before the engine, which had hitherto never run longer than 27 minutes, started to melt on its mountings.

Taking off at 1:02 p.m., Boothman ran the first lap in 5 1/2 minutes, averaging 343.1 mph and reaching nearly 380 mph in the straightaways. From then on, however, his average speed gradually went down, until his seventh lap average was 337.7 mph. By that time, uneven fuel consumption had altered the trim, causing his plane to list to the left, but that was not enough to stop him from streaking over the finish line and then making a triumphant circling turn over Calshot Castle to the sound of a cheering crowd and ships’ bells and whistles.

The Schneider Trophy race had ended with a bang rather than a whimper after all — in only 47 minutes, Boothman had averaged 340.08 mph, establishing the Supermarine as the fastest airplane in the world. Later that month, Royce installed an engine capable of producing 2,600 hp for short sprints in S1595, and on September 29 Flight Lt. George H. Stainforth flew it on five straight 1.9-mile runs over Southampton Water, averaging 407.5 mph and at one point hitting 415.2 mph. The S.6B was the first airplane to pass the 400 mph mark.

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