SIAI — Società Idrovolanti Alta Italia: Italy's Pioneer of Flying Boats & Seaplanes
Before Alessandro Marchetti arrived, before the Schneider Trophy races, before the mass transatlantic formations — there was simply SIAI. Founded in 1915 as the Società Idrovolanti Alta Italia (Upper Italy Hydroplane Company), SIAI was born into the crucible of World War I with a single purpose: to build flying boats and seaplanes for the nascent Italian naval air arm. What followed was a decade of rapid, often dangerous, engineering progress that laid the foundations for everything Savoia-Marchetti would later achieve.
The SIAI pennant — a bold blue triangular flag bearing the company name and a white cross — became a familiar sight on the waters of Lake Maggiore, the Adriatic, and the Mediterranean. These were not glamorous aircraft. They were working machines, built for patrol, reconnaissance, torpedo attack, and the brutal demands of maritime warfare. But they were also the school in which Italian seaplane engineering learned its craft.
Corporate Context
SIAI was established near Sesto Calende on Lake Maggiore in northern Italy — a location chosen for its access to calm water for seaplane operations and its proximity to the industrial resources of the Po Valley. The company operated under the SIAI name through WWI and the early interwar period. Alessandro Marchetti joined in 1922, and the company progressively evolved into Savoia-Marchetti as his design influence grew dominant. The early SIAI types — the S-series flying boats — represent the pure founding era before that transformation.
The Aircraft — SIAI S-Series Flying Boats & Seaplanes
The SIAI S-series numbering was not strictly sequential by development order — some numbers were assigned to projects, prototypes, or variants that overlapped in timeline. The following catalogue covers all principal types:
| Aircraft | Type | Era | Notes |
|---|---|---|---|
| SIAI S.8 | Reconnaissance flying boat | WWI (1917) | Single-engine biplane flying boat; Regia Marina patrol and reconnaissance duties over the Adriatic |
| SIAI S.9 | Training flying boat | WWI (1917) | Two-seat trainer variant; used to build Italian naval aviator numbers during the war |
| SIAI S.12 | Torpedo bomber flying boat | WWI–Interwar (1918) | Large biplane flying boat designed for torpedo attack; one of Italy's first purpose-built naval strike aircraft |
| SIAI S.13 | Racing & record seaplane | Interwar (1919) | High-speed floatplane; competed in early postwar air races; forerunner of the Schneider Trophy racing tradition |
| SIAI S.16 | Reconnaissance / passenger flying boat | Interwar (1919–1920s) | Versatile biplane flying boat used for both military patrol and early civil passenger routes; exported to several operators; one of SIAI's most successful early types |
| SIAI S.17 | Racing seaplane | Interwar (1920) | High-speed floatplane racer; developed from S.13 experience; competed in international speed contests |
| SIAI S.19 | Racing seaplane | Interwar (1920) | Further development of the racing floatplane line; part of Italy's systematic pursuit of air speed records in the early 1920s |
| SIAI S.21 | Racing flying boat | Interwar (1921) | Notable as the aircraft flown by Roald Amundsen's associate in early polar exploration support flights; also a Schneider Trophy entrant; twin-engine configuration |
| SIAI S.22 | Passenger flying boat | Interwar (1922) | Civil transport flying boat; early Italian commercial aviation on Mediterranean routes; transitional type as Alessandro Marchetti's influence began to shape the company |
| SIAI S.23 | Passenger / transport flying boat | Interwar (1922–1923) | Enlarged development of the S.22; multi-passenger civil flying boat; among the last pure SIAI types before the Savoia-Marchetti era fully took hold |
Engineering Character
The SIAI S-series aircraft share a common engineering DNA: biplane flying boat or twin-float seaplane configuration, wooden or mixed construction with fabric covering, water-cooled inline or rotary engines, and an emphasis on seaworthiness over outright performance. These were aircraft designed to operate from open water in all conditions — a demanding requirement that shaped every structural and aerodynamic decision.
The progression from the S.8 patrol boat of 1917 to the S.21 racing flying boat of 1921 illustrates how rapidly Italian seaplane engineering advanced in just four years — driven by the competitive pressure of international air racing and the hard lessons of wartime operational use.
Historical Significance
The SIAI S-series represents the founding chapter of what would become one of Italy's most important aviation lineages. Without the engineering knowledge accumulated in these early flying boats, Alessandro Marchetti would not have had the platform to develop the S.55 — the iconic twin-hull flying boat that carried Balbo's formations across the Atlantic — or the racing seaplanes that challenged Britain's Supermarine for Schneider Trophy supremacy.
For aviation historians and documentation collectors, these early types are among the rarest and most difficult to research. Primary technical documentation is scarce, often surviving only in Italian military archives or private collections. Where documents exist, they represent irreplaceable primary sources for understanding the birth of Italian naval aviation.
Technical Documentation at Online Aviation Library
Online Aviation Library maintains a growing collection of SIAI historical documentation. Given the rarity of surviving primary sources for these early types, our collections focus on what can be reliably authenticated and structured — prioritising accuracy over volume. As additional documentation is acquired and verified, collections are updated with free lifetime access for all purchasers.
If you hold or know of surviving SIAI S-series technical documentation, we welcome contact through the Online Aviation Library website.
This digital compilation, structure, indexing and presentation are © Sicuro Publishing.