How Mail Made Commercial Aviation

Curtiss JN-4D

The first plane the Airmail Service used was a modification of the Curtiss JN-4D, better known as the “Jenny.” This wooden biplane was also the first trainer plane for many military and civilian pilots and one of the first mass produced planes. While successful for military use, it had to be modified for the mail. The front seat was replaced with a mail compartment and a larger Hispano-Suiza Motor was added for more range. The ship was designated the JN-4H. Jennies were loved and hated and could be a nightmare to fly. One pilot noted that “It is best not to inspect this ship. If you do, will never get in it.”¹

The Airmail Service was originally operated by army pilots, who were familiar with the Jenny from its use as a trainer. Major Reuben Fleet, in charge of the first flights, was given six Jennies,² and oversaw the conversion of them from JN-4D to JN-4Hs. They were used, first by the army pilots, than beginning on August 12, 1918, by Post Office Department pilots, who continued to use them until 1921.

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Standard JR-1B

When the Post Office Department took charge in August 1918, they had already ordered six Standard J planes that were modified into Standard JR-1B mail planes, making them the first planes designed with airmail in mind. While only used for a short time, they proved reliable for their short stint. The Standard JR-1B was capable of holding 180 lbs. of mail and flying at a top speed of 95 mph.³ Postal officials with their eyes now on a New York – Chicago route were already seeking planes with a longer range.

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Curtiss R-4LM

The Post Office Department also used the Curtiss R-4LM in their first year of operations. The R-4LM fleet was six planes strong and like the Standard JR-1B, used for a relatively short time. The Curtiss R-4LM was a modified version of the Curtiss Model R, with its front cockpit converted into a cargo hold. The R-4LM proved quite capable and could carry 400 lbs. of mail at a maximum speed of 95 mph. All three of these early planes would soon be replaced by what became the longest-lasting plane in the airmail service, the deHavilland DH-4B.

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deHavilland DH-4

The Dayton-manufactured deHavilland DH-4 (with modifications and a name change to DH-4B) would become the aircraft that built the airmail service, with over 100 planes in use. The plane was first given by the army to the Post Office as war surplus. The DH-4 had been a successful military aircraft, but as the Post Office discovered after several flights, it needed several alterations before becoming a successful airmail plane. As an airmail plane, the DH-4 had many inherent problems, including a weak frame, poor wing fabric, and landing gear that was too frail for its new mail-carrying weight.⁴ The plane was improved with a sturdier, stronger fuselage, a move of the gas tank forward for balance, and a switch of the pilot’s seat from front to back.

The changes had many advantages, not the least of which were crash survival rates (pilots were no longer trapped in crashes between an engine and exploding gas tanks in front and hundreds of pounds of flammable paper in the mail bags in the back). The deadly crash rate of the DH-4s resulted in five deaths in 1920,⁵ giving it the nickname the “Flaming Coffin.”⁶ The greatly altered plane was dubbed the DH-4B. The DH-4B could hold 500 lbs. of mail and fly as far as 350 miles. The DH-4B also had a lengthened exhaust pipe that kept smoke out of pilot’s faces. The DH-4B was beloved by the pilots for its reliability and control.

From its beginning the airmail service was blazing a trail into the unknown, one of the men charged with making it work was Second Assistant Postmaster General Otto Prager. To accomplish this Prager needed bigger and better planes. By the winter of 1919 he was desperate to show Congress that the service could operate on a regular basis between the nation’s two commercial centers – New York and Chicago. If he could not prove that his planes were faster than trains between the two cities, Praeger risked Congressional disapproval, and the end of their willingness to finance the service. Unfortunately, Praeger’s search for faster planes led him to purchase some of the worst planes the service would use. While fast, the Martin MB-1, Twin-DH, and Junkers JL-6, as used by the airmail service were deadly mistakes.

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Martin MB-1 Bomber

At first, Prager thought the answer might be in another military plane. The Martin MB-1 Bomber was well thought of by both army and civilian aviators. As used by the Post Office Department it was designated the Martin mail plane. The Martin was chosen for its massively larger carrying capacity of 1,500 lbs. of mail. The plane also had a superior range of 490 miles compared to deHavilland’s 350 miles. The plane was costly at $31,000 per plane in 1919. The cost was too much for the Post Office Department and as popular as it might be, Praeger just could not afford it. It also may not have helped that mechanic Neal Montis was killed and pilot J.P. Harris severely injured in a Martin as the plane’s motor stopped on takeoff, the plane crashing into the field in Cleveland.

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Twin-DH

Prager was convinced that the popular DH-4Bs could be modified and improved. The modified planes were known as the J-2 or Twin-DH. The Twin-DH was a DH-4B with two Liberty 400 hp motors, one mounted on each wing. The modified deHavilland was radically cheaper, at $7,000.⁷ The modifications allowed the Twin-DH to hold more mail, doubling both speed and range. But it was a failure. Introduced early 1920, the Twin-DH planes could only be flown for short distances before excessive vibration problems led to snapped wings and forced landings.⁸ Pilot Kenneth Stewart was killed while flying the Twin-DH. That and other crashes, fortunately not fatal, led to its retirement in February 1921. In his enthusiasm for the new plane, Praeger had ordered twenty DH-4B planes turned into Twin-DHs. He was forced to ground the remaining planes and ordered them converted back into DH-4Bs.

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Junkers-Larsen JL-6

Praeger’s third selection was a modification of the Junker F-13, an all-metal single wing aircraft successful in Europe. The plane was brought to the US by John Larson Aircraft and produced under a new name, the Junkers-Larsen JL-6. Praeger ordered eight planes for $200,000 in 1920.⁹ The JL-6 used a 185 hp BMW engine, held 1,500 lbs. of mail, and flew at a speed of 100 mph. What seemed like a find would prove to be one of the biggest mistakes in the life of the airmail service. From the start the plane was plagued with problems. The airmail service’s first pilot, Max Miller, noted the plane’s excessive vibration in flight and stated that the plane was very slow.¹⁰ The plane also suffered in test flights, with nine forced landings, four due to leaking fuel lines.¹¹ Despite these problems, Prager was desperate to get the plane in to service in time for the planned transcontinental routes.

One JL-6 plane crashed near Toledo, Ohio. The pilot survived with severe burns. On September 1, 1920, Miller and airmail mechanic, Gustav Reirson, were killed when their JL-6 caught fire in mid-air and crashed. The plane suffered a known fuel leak problem.¹² After that crash the remaining JL-6 planes were temporarily grounded, but returned to use the following February. Almost immediately Praeger regretted his error. On February 9, 1921, pilots Hiram Rowe, William M. Carroll and mechanic R.B. Hill were flying a JL-6 airplane when it caught fire in midair and exploded upon crashing at Lacrosse, Wisconsin. All three men were killed before help could reach them.  At last the JL-6 planes were permanently grounded. No known American Junker-Larson JL-6s exist today, the rest were either scrapped or lost in a warehouse fire.

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Douglas M Family

The next plane purchased by the Post Office Department was the Douglas M-1. As aging DH-4Bs became more expensive to maintain, the airmail service called on airplane manufactures in 1925 for bids on a new plane. The winner was the Douglas Aircraft Company with their Douglas M-1. The plane was superior to the DH-4B as it could fly faster and carry twice as much mail. The plane was put into service in 1926. The plane was successful enough that modified versions followed - the Douglas M-2, M-3, and M-4. The Post Office ordered forty M-4s, ten M-3s, and one M-2.

The planes were the last ones ordered by the Post Office Department. The Air Mail, or “Kelly Act” of 1925 signaled the end of the government controlled airmail service.¹³ It paved the way for the growth of commercial airlines and planes that would carry not just mail, but also passengers. The Douglas planes were used by the Post Office until private contractors began taking over in 1926 and 1927. Many of the Douglas mail planes were sold to private mail carriers such as National Air Transport (NAT) and Western Air Express.

The commercial airmail routes were designated by number and known as Commercial Airmail (CAM) Routes. The first five CAM routes were contracted in 1925 to Colonial Air Transport, Inc. (Boston and New York); Robertson Aircraft Corp. (Chicago and St. Louis); National Air Transport, Inc. (Chicago and Dallas); Western Air Express, Inc. (Salt Lake City and Los Angeles); and Walter T. Varney (Elko, Nevada, and Pasco, Washington). Contracted airmail service proceeded slowly over the next two years. The Post Office retained control of the transcontinental New York – San Francisco route, making its last flight on that route on September 9, 1927.

The new companies hired some of the government pilots to fly the routes and purchased many of the government planes. But as the companies looked to expand their routes and add passengers, they began ordering new aircraft, sparking a growth in the nation’s aircraft industry.

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Curtiss Carrier Pigeon

The Curtiss Carrier Pigeon was designed specifically for airmail service. It was one of the first aircraft built with night flying in mind.¹⁴  Ten Pigeons were purchased by National Air Transport (NAT). The Carrier Pigeon was slower than the Douglas M-2 but capable of carrying the same amount of mail. It was used on NAT’s nighttime CAM routes. The plane helped NAT succeed on their CAM 3 route beginning on May 12, 1926.¹⁵ The Carrier Pigeon was used again by NAT to open their second route, CAM 17 in September 1927 between New York and Chicago.¹⁶ The Carrier Pigeon was retired in 1929 and replaced with faster Curtiss models.

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Ford 5-AT

The Ford 2-AT was an iconic plane of the interwar period in airmail history. In 1924 Henry Ford announced that his Ford Motor Company would enter the airplane business. Ford had purchased Stout Metal Air Plane Co. and with their lead engineers produced the Ford 2-AT, an all metal monoplane. The plane utilized elements from earlier planes (such as the infamous Junkers JL-6) to produce its successful design. The plane was nicknamed the “Tin Goose” by the newspapers for its metal corrugated skin.¹⁷ The 2-AT could carry as much as 1280 lbs. of mail and fit six passengers comfortably.¹⁸ The 2-AT was mainly used by Ford for their two CAM routes, CAM 6 (Detroit and Dearborn, Michigan to Cleveland, Ohio), and CAM 7 (Detroit and Dearborn to Chicago). They were used on these routes from February 16, 1926 until July 1928 when Ford sold the routes to Stout Air Company. The 2-AT was replaced by its bigger brothers the Ford 4-AT and 5-AT. The Ford 4-AT, introduced in 1926, was based on the 2-AT but with the addition of two motors placed on the wings, giving it the distinctive nickname “Tri-motor.” The plane was a commercial success. The Tri-motor could carry 1725 lbs. of mail and 11 passengers. The 4-AT had the advantage of over 900 hp thanks to its three Wright J-6 Motors.¹⁹ The plane was used by several airlines, including Trans World Airlines, Texas Air Transport, American Airlines, United, Ford’s own airline, and Pan American World Airways. It was one of the first planes to be commonly across the airline industry.

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Waco 9

The Waco 9 put Waco Aircraft Company on the map with its large production run of 276 planes. It was favored by barnstormers and for general purpose flying.²⁰ The Waco 9 was a slow plane, considered underpowered with a 90 hp Curtiss OX-5 motor, and known to roll over on its back very easily.²¹ Despite these problems the plane sold well and led to later models such as the Waco 10. The plane had a range of 375 miles and could carry 385 lbs. of mail. Clifford Bell used three Waco 9s on his CAM 11 route (Cleveland, Ohio to Pittsburgh, Pennsylvania). The Waco 9s were flown as late as 1934.

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Swallow OX-5

The Swallow OX-5 biplane, also known as the “New Swallow,” was first introduced in 1924 by the Swallow Airplane Manufacturing Company. The plane was small, with a 90 hp Curtiss OX-5 motor, could carry only 360 lbs. of mail, and had a range of 500 miles.²² The plane was used extensively by Walter T. Varney for Varney Air Lines. His company used six Swallows on CAM 5 (Elko, Nevada and Pasco, Washington). The Swallows began flying the route on April 6, 1926 and were used until it was acquired by United Airlines.²³

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Pitcairn PA-5 Mail Wing

The Pitcairn PA-5 Mail Wing was the first of the Mail Wing series. The plane was used by the Post Office at the end of their operations in 1927. Private contractors operating some of the new CAM routes purchased some of the planes, including Texas Air Transport (TAT) for CAM 21 (Dallas and Galveston, Texas), and CAM 22 (Dallas and San Antonio, Texas). The Pitcairn Company also ran its own mail routes and used eight PA-5s on CAM 19 and 25.²⁴ The PA-5 was also used by Eastern Airlines after they acquired Pitcairn’s CAM routes in 1930. Eastern retired the planes in 1934. A few PA-5s were used by NAT on CAM routes 3 and 17. As its name suggest, the Pitcairn PA-5 Mail Wing was built as a mail plane. It could hold 500 lbs. of mail, which was less than some of its competitors at the time. It could reach a speed of 130 mph. The plane would lead to later Pitcairn models such as the Pitcairn PA-7 Mail Wing.

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Boeing Model 40

The Boeing Model 40 was constructed as a mail plane in 1925, intended to replace the Post Office deHavillands. It was used on Boeing’s CAM 18 (Chicago, Illinois and San Francisco, California).  Boeing Air Transport also used the next plane in the series, Model 40A, on CAM 18 between 1927 and 1934.²⁵ The Model 40A had a 525 hp single Pratt and Whitley “Hornet” motor and could carry 800 lbs. of mail and passengers for 535 miles on a tank of gas. A later model, the 40B had a bigger cabin and could carry four passengers. Thirty-eight 40B planes had been built by 1929. The planes were produced until 1932 when newer models such as the Boeing Monomial and Boeing model 80 were built.

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Travel Air 5000

A more obscure mail plane was the Travel Air 5000, introduced in 1927. The plane was built by the Travel Air Manufacturing Company and only 14 were produced. The plane was mainly used by National Air Transport, which bought five planes for use on CAM 3 in 1927. The plane had an impressive 675-725 miles range and could carry 750 lbs. of mail along with five passengers.²⁶ One of the Travel Air 5000 planes, nicknamed the “Woolaroc,” gained fame for winning the infamous 1927 Dole Air Race²⁷ from Oakland to Hawaii. It survives today as one of two Travel Air 5000s. National Air Transport retired its Travel Air 5000 in 1930.

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Pitcairn PA-7S Mail Wing

In 1930 Pitcairn improved their PA-5 Mail Wing with the PA-7M. The PA-7M, also known as the Super Mail Wing, could carry 636 lbs. of mail and flew faster than the PA-5 at 135 mph. The plane used a J6 Wright 240 hp motor. Pitcarin used the PA-7M on CAM 19 (New York City and Atlanta, Georgia). Only eight PA-7Ms were made. Their production was cut short by the production of the new PA-8 only a few months later.

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Boeing 221 Monomail

Boeing took a leap into the future of aviation in 1930 with the Monomail. This aircraft was ahead of its time, with retractable landing gear, a smooth streamlined body, and single wings set off from the bottom of the fuselage. The remarkable design, however, was more advanced than the engines or propellers of the age. Only two Monomail planes were ever built, models 200 and 221. The Monomial 200 was an all-cargo mail model that could carry 2280 lbs. of mail at 158 mph.²⁸ The Monomail 221 carried six passengers and 750 lbs. of mail.²⁹ Both planes had 575hp Pratt and Whitney “Hornet B” motors, a lit instrument panel, and shock absorbers in the landing gear.

Both the 200 and 221 Monomail planes were converted into model 221A for transcontinental passenger services. That model could hold eight passengers. The original Monomail 200 had been converted into a 221A before it crashed in 1935. The other plane was likely retired and scrapped by Boeing after 1933.

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Sikorsky S-42

The Sikorsky S-42 was one of the first commercially successful seaplanes. The US Navy experimented with the seaplanes and private manufacturers for years and a few were used in early flights between Florida and Cuba. The S-42 was introduced to the public by Pan American airways in 1934. The plane was quite powerful thanks to its four 750hp Pratt and Whitney motors.³⁰ A Sikorsky S-42 could carry 2,000 lbs. of mail along with 36 passengers.³¹

The plane was used by Pan American World Airways on routes between Miami and South America on their Foreign Airmail (FAM) 5 (Miami and Central and South America) and FAM 17 (Baltimore, Maryland and Bermuda). These planes showed how luxurious flying could be. The S-42 had full sized beds for passengers, a complete kitchen and staff who could cook three course meals.³² The plane could reach 190 mph and set a flight record between Hawaii and San Francisco, California of 17 hours and 57 min on a survey flight to China in 1935.³³ No S-42s survive today. Six have crashed and sank and the other four were scrapped by Pan Am after the adoption of later clipper models such as the Martin M-130. There are a few cousins of the S-42s in museums across the US such as the Sikorsky S-39s, S-40s, and S-43s.

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Douglas DC-3

The Douglas DC-3 is an iconic plane that marked the explosion of commercial air travel in the US and the final transition for airlines from a reliance on mail to passengers for paying their bills. The Douglas DC-3 originally flew in 1935 and was quickly adopted by airlines across the country. The plane demonstrated how far Douglas had come since the M-2 and how rapidly aircraft technology had evolved in ten years. The plane could carry 28 passengers and 2083 lbs. of mail at 183 mph.³⁴ American Airlines purchased 37 DC-3s as the foundation of its iconic “Flag ship Fleet” in 1937.³⁵ Pan Am used the DC-3 for its North American routes. United Airlines had six DC-3s that were used as late as 1956. By 1938, 95 percent of the planes flying in commercial air traffic were DC-3s.³⁶

By 1936 the aims of the Kelly Act finally came to fruition. What had begun in 1918 as a government operation to move mail across the country faster had transitioned in the late 1920s and early 1930s to the government, through the Post Office, assisting private companies in a quest to create a steady and broad commercial airlines service. Airlines that could barely survive in their early years found that airmail contracts not only kept them alive, but provided the funding to explore bigger and better airplanes, airplanes that could finally rely on passengers for the bulk of their revenues. Without the Post Office and its mail contracts, the nation’s commercial aviation system and airline manufacturers would not have become the giants of American industry that they are today.