Douglas Dolphin

The Douglas Dolphin was an amphibious flying boat. While only 58 were built, they served a wide variety of roles: private "yacht," airliner, military transport, and search and rescue.

Design and development
The Dolphin originated in 1930 as the "Sinbad," a pure flying boat without wheels. The Sinbad was intended as a luxurious flying yacht. Undaunted by the lack of demand, Douglas improved the Sinbad in 1931 so that it was amphibious, and could land on water or land. The improved aircraft was named "Dolphin", however this did not represent the end of development, as many detail improvements were made, including an increase in the length of over a foot and several changes were made to the empennage, engine nacelles and wings. The Great Depression had curtailed demand for such extravagance as a "flying yacht", but Douglas managed to interest the United States Coast Guard who not only bought the Sinbad, but 12 Dolphins.

Operational history
The first two were purchased by Wilmington-Catalina Airlines to fly passengers between Los Angeles and Santa Catalina Island, becoming the first successful Douglas airliners. Subsequent examples were ordered by the United States Navy and U.S. Coast Guard for use as transports and search and rescue craft. The U.S. Army Air Corps ordered several under the designations C-21, C-26, and C-29. Many were eventually ordered for their original purpose as luxury transports. Owners included William Boeing, the founder of the Boeing Company, and Philip K. Wrigley, the son of the founder of the Wm. Wrigley Jr. Company. William K. Vanderbilt bought two with custom interiors for use from the Vanderbilt yacht Alva as flying tenders.

One was procured by the U.S. Navy as a transport for President Franklin D. Roosevelt. Although never used by Roosevelt, this was the first aircraft procured to provide transportation for the President of the United States.

In 1933, landing in heavy seas, the USCG RD-4 undertook some rescues of merchant sailors at sea, feats that made spectacular news reports, enthralling the American public.

Variants
Data from:McDonnell Douglas Aircraft since 1920 Vol.1
 * Douglas Sinbad
 * The original prototype built as a flying boat, intended to be a luxurious flying yacht, first flown in July 1930. No orders were received for the Sinbad which was eventually bought by the U.S. Coast Guard.


 * Dolphin Model 1
 * The initial two Dolphins built for the Wilmington-Catalina Airline Ltd. as six-seat airliners.


 * Dolphin Model 1 Special
 * The Model 1s re-designated after modification to seat eight passengers.


 * Dolphin Model 3
 * The third commercial Dolphin built as a luxury transport named Lesgo with seats for two crew and four passengers for Powell Crosley Jr., powered by 2x 300 hp Pratt & Whitney Wasp Junior A engines. Later impressed into the RAAF as A35-3.


 * Dolphin 113
 * One aircraft named Jade Blanc V for French clothing manufacturer Armand Esders (who also owned a Bugatti Royale) similar to the RD-4, powered by 2x 550 hp Pratt & Whitney R-1340-S1H1 Wasp engines.


 * Dolphin 114
 * A single Dolphin built to order for Philip K. Wrigley, powered by 2x 450 hp Pratt & Whitney Wasp SC1 engines.


 * Dolphin 116
 * One aircraft for the Armada Argentina (Argentine Navy), powered by 2x 450 hp P&W R-1340-96.


 * Dolphin 117
 * One aircraft initially named Rover, bought by William E. Boeing, which ended up in CAA (forerunner of the current Federal Aviation Administration) service. Sole surviving example, painted in USCG markings.


 * Dolphin 119
 * Two aircraft built for A.G. Vanderbilt II and W.K. Vanderbilt II and operated from the yacht Alva. One of the two (which is unknown) joined the RAAF as A35-2.


 * Dolphin 129
 * Two aircraft ordered by Pan American Airways for its subsidiary (at that time) China National Aviation Corporation, powered by 2x 450 hp Pratt & Whitney Wasp S3D1 engines. One crashed in heavy seas and the other was destroyed during or shortly after the Japanese invasion of China.


 * Dolphin 136
 * A single Dolphin, powered by 2x 450 hp Pratt & Whitney Wasp Junior SB engines, ordered by Standard Oil and later impressed by the RAAF as A35-1.


 * FP-1
 * Several C-21 aircraft loaned to the U.S. Treasury Department for border patrols during Prohibition.


 * FP-2
 * The two Y1C-26 Dolphins during a brief attachment to the U.S. Treasury Department.


 * FP-2A
 * The designation used by those Y1C-26A aircraft that were attached to the U.S. Treasury Department.


 * FP-2B
 * The two C-29s when in use by the U.S. Treasury Department.


 * RD-1
 * One aircraft, powered by 2x 435 hp Wright R-975E radial engines, operated by the U.S. Navy.


 * RD-2
 * Four Dolphin aircraft of two distinct types. 1 Aircraft similar to the Y1C-21 and powered by 2x 500 hp Pratt & Whitney R-1340-10 engines, for the U.S. Coast Guard. Two were U.S. Navy VIP staff transports similar to the Y1C-26 powered by 2x 450 hp Pratt & Whitney R-1340-96 engines. The final aircraft was completed for the U.S. Navy as the first presidential aircraft, for Franklin D. Roosevelt, powered initially by 2x 410 hp Pratt & Whitney R-1340-1 engines and later by 2x 500 hp Pratt & Whitney R-1340-10 engines, seating five though it was reportedly never used by the President.


 * RD-3
 * A utility transport version of the RD-2, six of which were built for the U.S. Navy, powered by 2x 500 hp Pratt & Whitney R-1340-4 or by 2x 500 hp Pratt & Whitney R-1340-96 engines.


 * RD-4
 * Ten aircraft for the U.S. Coast Guard, powered by 2x 420 hp Pratt & Whitney Wasp C1 engines.


 * OA-3
 * C-21 aircraft re-designated.


 * OA-4
 * C-26 aircraft re-designated.


 * OA-4A
 * Y1C-26A aircraft re-designated.


 * OA-4B
 * C-26B aircraft re-designated, one of which was fitted with an experimental fixed tricycle undercarriage.


 * OA-4C
 * Four OA-4A and one OA-4B aircraft modernized in 1936.


 * Y1C-21
 * Eight aircraft for the USAAS, similar to the Navy's RD-1, powered by 2x 350 hp Wright R-975-3 engines.


 * Y1C-26
 * Two aircraft for the USAAS with increased dimensions, fin area and fuel capacity (from180 USgal to 240 USgal). Powered by 2x 300 hp Pratt & Whitney R-985-1 engines.


 * Y1C-26A
 * Eight aircraft for the USAAS differing from the Y1C-26 only in minor details.


 * C-21
 * Y1C-21 aircraft re-designated.


 * C-26
 * Y1C-26 aircraft re-designated.


 * C-26A
 * Y1C-26A aircraft re-designated.


 * C-26B
 * Four aircraft powered by 2x 400 hp Pratt & Whitney R-985-9 engines.


 * C-29
 * Two Dolphins, powered by 2x 550 hp Pratt & Whitney R-1340-29 engines, were essentially similar to the Y1C-26As.

Military operators

 * Argentina
 * Royal Australian Air Force
 * U.S. Army Air Corps
 * U.S. Army Air Force
 * United States Coast Guard
 * U.S. Marine Corps
 * United States Navy
 * United States Coast Guard
 * U.S. Marine Corps
 * United States Navy