Born in Zibido San Giacomo, Castoldi worked for the experimental center of Italian Military Aviation at Montecelio, not far from Rome. In 1922 he moved to Macchi Aeronautica, where he became famous for designing a series of seaplanes that set world speed records. His first winning plane was the Macchi M.39 seaplane. It was designed in 1925-26 to compete in the Schneider Trophy race of 1926. Powered by a Fiat engine it managed a top speed of 396 km/h and won the contest for that year. For the next four years, Castoldi designed several more racing seaplanes which entered the Schneider Trophy races but they lost to the British racers. Castoldi's most famous plane was the Macchi M.C.72. At first, Castoldi hoped this plane would enter the Schneider Trophy race of 1931 but the plane could not be ready in time for that contest. As a result of three consecutive victories for the British, the Schneider races were over. But development on the M.C.72 continued. Jane's asserts that the Italian dictatorBenito Mussolini personally supported the M.C.72 program. Despite many setbacks, including the deaths of two test pilots who were flying the plane, the project continued and the plane got faster. In April, 1933 pilot Francesco Agello succeeded in setting a speed record for a seaplane with a speed of 684 km/h. Still, work on improving the plane's speed continued as the design team hoped they could exceed a speed of 700 km/h. After a year and a half, this feat was accomplished as Agello, flying three passes in the M.C.72, attained an average speed of 709 km/h on October 23, 1934. This world speed record lasted for five years – but as a record for a piston-engine seaplane it has never been broken. After the M.C.72, Castoldi worked on designs for Italian fighters. However, he was limited by the inability of Fiat to provide more powerful engines. Later designs had to rely on German supplied engines. Castoldi was in charge of the design of a series of military fighter that formed the mainstay of Italian fighter force in World War II, specifically the C.200, C.202 and Macchi C.205. In 1945 Castoldi retreated to private life. He died at Trezzano sul Naviglio in 1968.
