A small two-cylinder hand-started auxiliary power unit mounted in the fuselage below the cockpit generated compressed air used to start the main engines.

[2] After the S-35 crashed and was destroyed in September 1926, Sikorsky built the first S-37 registered as X1283 for Rene Fonck to make another attempt at a non-stop Atlantic crossing and win the Orteig Prize.

The Jupiter engines were exchanged for 525 horsepower (391 kilowatts) Pratt & Whitney Hornets, then Fonck's sponsors sold it to American International Airways of Argentina where it was renamed the Southern Star and re-registered as R1283.

During its delivery flight on 30 June 1929, it became the first commercial transport to cross the 18,700 feet (5,700 m) high Andes mountains between Buenos Aires and Santiago carrying a payload of 5,100 pounds (2,300 kg) including eight people.

Later called the VS-37B Guardian, it was equipped with Pratt & Whitney Hornet engines and a redesigned tail that eliminated the adjustable center vertical stabilizer and increased the size of the rudders.