Still looking like something from science-fiction today, the S.55X incorporated twin hulls on a thick-section wing, powered by a pair of Asso 750 powerplants mounted above the cockpit in the wing’s centre-section.
Inset: Another glorious Futurist poster celebrating Balbo’s Decennial transatlantic cruise to the USA in 1933. Bal bo was determined that Italy should be perceived as a technologically advanced nation, and saw the USA as a natural ally in his desire to extol the virtues - political and military - of aviation.

The S.55X was the only variant of the type to be powered by the Asso 750, as seen here in its distinctive configuration with a tractor engine at the front of the nacelle and a pusher at the rear, the propellers counter-rotating. Note the upward-pointing thrust-line of the nacelle, and the port wire-braced boom supporting the triple-finned tail.

A classic contemporary Italian poster celebrating Italo Balbo’s Crociera Aerea Del Decenniale (Decennial Aerial Cruise marking ten years since the formation of the Regia Aeronautica). He led 24 twin-Asso 750-powered SIAI-Marchetti S.55Xs in formation from Italy across the Atlantic to the Chicago World’s Fair in the USA during July-August 1933.

Isotta Fraschini was a supplier of engines for Italian bombers in the First World War, including the Caproni 450 (Ca 3).