S.55

The SIAI‑Marchetti S.55 was an Italian twin‑hull flying boat that first flew in 1924 and quickly became one of the most iconic seaplanes of the interwar period. Designed by Nicola Romeo’s SIAI (Società Idrovolanti Alta Italia) and later built by the merged SIAI‑Marchetti firm, the S.55 featured a distinctive double‑fuselage layout joined by a high wing and a single 450 kW (600 hp) Fiat A.12bis V‑12 engine mounted in a central nacelle and driving two tractor propellers via shafts. This configuration gave the aircraft excellent stability on water, a large internal payload capacity, and the ability to carry up to eight passengers or a full crew for record‑setting flights. Between 1925 and 1936 the type set numerous distance and endurance records, most famously the 1928 transatlantic crossing of the “Santa Maria” piloted by Italo Balbo’s squadron of twelve S.55s, a demonstration of mass formation over the ocean. The S.55’s success helped establish Italy’s reputation in long‑range maritime aviation, influenced later twin‑hull designs, and provided a practical platform for early commercial and military air‑mail services. Its innovative structure and record‑breaking achievements secured its place in aviation history.

SIAI-Marchetti

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