For the 12-liter racing inboards, in 1939 the title was not officially awarded even though a regular classification could be made on the basis of the results of the Coppa Re Imperatore (Venice), Gold Cup (Detroit) and President's Cup (Washington); however, we consider the following recognition to be historically honest. From "Almanacco della Motonautica", 1963: " During the motorboat meeting of 1 and 2 July 1939 in Venice the world championship of the 400-kilo inboards was proposed again. Unfortunately, only two drivers were competing for the title, namely the Italians Achille Castoldi and Rusconi. Easy final success for Castoldi and his Picchiotti-Alfa Romeo, while Rusconi was the victim of a sinking."

Among the curiosities, since the championship was disputed in two heats, in the second, given the sole presence of Castoldi, he was joined by the 1000cc racing outboards.
Incredible but true, Augusto Romani with his Riva Soriano, went on to win by establishing a speed of 71.556 km/h against the 70.978 of Castoldi's Alfa Romeo.
In the 1963 Powerboating Almanac this quote is reported: "In 1939 the 400 kilo title was not officially assigned, even though the race was held regularly, here too we consider the following recognition historically honest"