Sikorsky S-40 Clipper

The Sikorsky S-40 was an American amphibious flying boat built by Sikorsky in the early 1930s for Pan American Airways.Sikorsky designed the S-40 in response to a request from Juan Trippe, president of Pan American Airways, for a larger passenger carrying airplane. The S-40 could carry 38 passengers, a significant increase over the S-38's capacity of eight passengers.Despite its significant size and capacity increase over the preceding S-38, the S-40 design was a conservative iteration of the smaller aircraft;[3]: 62  the numerous flying wires and strut braces that were used as an exterior support framework caused significant drag and prompted Charles Lindbergh, retained as a consultant for Pan American, to tell Sikorsky "it would be like flying a forest through the air."[4][5]: 57  Only three were built as Sikorsky began designing the more advanced and streamlined S-42 to replace the S-40 shortly after the latter entered revenue service,[3]: 62–63  based partly on input from Lindbergh.Passenger carrying service was initiated on November 19, 1931.The S-40 was Pan American's first large flying boat. American Clipper served as the flagship of Pan Am's clipper fleet and this aircraft model was the first to earn the popular designation of "Clipper" or "Pan Am Clipper".[12] The three S-40s served without incident during their civilian lives, flying a total of over 10 million miles.

They were retired around 1940 and turned over to the US Navy during World War II, who used them as trainers for four-engined flight instruction. Under Navy service, the aircraft were designated Sikorsky RS-4.[13] All three of the S-40s were eventually scrapped, starting in 1943.