The S.55 prototype flew in 1925, in an era still committed to the biplane flying-boat, it had a cantilever shoulder-wing monoplane with twin hulls and delicate booms supporting a twin-fin triple-rudder tail assembly. Side-by-side pilots' cockpits were located in the leading edge of the wing centre-section. Twin tandem engines were carried on struts over the wing.
The S-55 was basically a torpedo-bomber, pow-ered by two 700 hp Fiat A-24R engines in tandem, but the 1933 version, designated S-55X was specially cleaned-up and fitted with 559kW / 800 hp Isotta-Fraschini Asso-750 engines. The two pilots sat side-by-side in the centre-section, under the engines. The S-55 had open gun-positions in the front and rear of each hull, but these were faired over in the S-55X.
Total production exceeded 200. The type formed the main equipment of Italy's maritime-bombing squadriglie for many years, 13 remaining on charge (but in reserve) in 1939. The S.55C and S.55P civil passenger versions operated Mediterranean routes for a decade.
The S.55 achieved great fame through spectacular long-distance flights: Lieut-Col the Marchese de Pinedo flew the Santa Maria from Sardinia to Buenos Aires and then through South America and the USA in 1927.
General Italo Balbo conceived in 1930 the idea of making a mass flight in formation over the Atlantic, at a time when transatlantic flying was still a hazardous adventure. A fleet of twin-hull flying-boats was ordered from the Savoia-Marchetti company for the attempt, and the first began in December 1930 when specially modified S.55As covered 10,400km between Italy and Brazil.
Balbo led twelve of these in person across the South Atlantic from Rome to Rio de Janeiro. In 1933, he led an even greater armada of 24 similar machines across the North Atlantic, from Rome to Chicago by way of Iceland, Greenland and Labrador, and back again to Rome via New York, the Azores and Lisbon. The 24 S.55X machines overflew the Alps and continued in stages via Iceland, Greenland and Labrador to Chicago for the 1933 Century of Progress Exposition. The international press coined the phrase 'Aerial Armada' to describe the flights. Neither flight was achieved without loss of life, but from that moment the idea of an airline service across the Atlantic no longer seemed such a remote possibility.
Engines: 2 x 700 hp Fiat A-24R
Span 79 ft. 11 in
Length 54 ft. 2 in
Height 16 ft. 5 in
Wing area 990 sq. ft
Weight empty 11,440 lb
Loaded weight 16,940 lb
Max. speed 147 mph
Ceiling 13,776 ft
Max. range 2,174 miles
Engine: 2 x Isotta-Fraschini Asso 750R, 656kW
Max take-off weight: 8260 kg / 18210 lb
Loaded weight: 5750 kg / 12677 lb
Wingspan: 24.0 m / 79 ft 9 in
Length: 16.75 m / 55 ft 11 in
Height: 5.0 m / 16 ft 5 in
Wing area: 93.0 sq.m / 1001.04 sq ft
Max. speed: 279 km/h / 173 mph
Cruise speed: 233 km/h / 145 mph
Ceiling: 5000 m / 16400 ft
Range w/max.fuel: 4500 km / 2796 miles
Range w/max.payload: 2000 km / 1243 miles
Armament: 4 x 7.7mm machine-guns, 1 torpedo or 2000kg of bombs