Boeing YB-9 – A Precursor to Modern Bombers

The Boeing YB-9, a revolutionary all-metal monoplane bomber, stands as a testament to the transformative era of aviation in the early 1930s.

As the first of its kind in the United States, the YB-9 set a new standard for military aircraft design, showcasing advanced features that would shape the future of bomber aviation.

From its sleek and aerodynamic construction to its impressive performance capabilities, the YB-9 marked a significant milestone in the evolution of aerial warfare.

In this article, we delve into the design and operational history, exploring the impact it had on subsequent bomber aircraft.


Design & Development

The genesis of the Boeing YB-9 was a response to the United States Army Air Corps’ (USAAC) requirement for an all-metal monoplane bomber that could outrun contemporary fighter aircraft.

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Boeing’s proposal was based on their Model 214, itself a militarized adaptation of the Boeing Model 200 Monomail.

The Model 200 Monomail.
The Model 200 Monomail.

The Model 200 Monomail was a mail plane produced in the early 1930s. This groundbreaking aircraft marked a departure from the traditional biplane design, featuring an all-metal, low-wing, cantilever monoplane configuration.

Its name, “Monomail,” is a nod to its primary intended role as a mail plane.

The Monomail was ahead of its time, integrating a streamlined fuselage and a retractable undercarriage, both features that would become standard in aircraft design but were innovative at the time of its introduction.

Its smooth, unbroken lines and sleek aerodynamic design were a significant improvement over the rough, drag-inducing surfaces common in aircraft of the era.

The Monomail was powered by a single Pratt & Whitney Hornet engine, enclosed in a NACA cowling, another forward-thinking design feature that would become widespread in later years.

The Model 210.
The Model 221.

The NACA cowling helped reduce drag and thus improved the aircraft’s overall performance.

The first Model 200 Monomail flew in May 1930. It carried mail between Chicago and San Francisco for Boeing’s own airline, Boeing Air Transport (which would later become part of United Airlines).

Boeing introduced a larger, more capable version of the Monomail, the Model 221, in 1931. This variant was equipped with a more powerful engine and was configured to carry six passengers in an enclosed cabin in addition to mail.

However, despite its technological innovations, the Monomail was not widely adopted.

This was primarily due to the lack of suitable variable pitch propellers, which limited the Monomail’s performance. Only two Monomail aircraft were built: one Model 200 and one Model 221.

Though the Monomail didn’t achieve commercial success, its design ideas greatly influenced future aircraft.

Boeing incorporated the lessons learned from the Monomail into their B-9 bomber and the famous Boeing 247, often considered the first modern airliner.

Thanks to the Monomail the YB-9 was the first bomber in the USAAC’s inventory to fully incorporate advanced features such as an all-metal construction, a streamlined aerodynamic design, retractable landing gear, and closed cockpits.

It was a low-wing, cantilever monoplane powered by two direct-drive Pratt & Whitney R-1860 Hornet B radial engines, each producing 600 horsepower.

The aircraft measured approximately 53 feet in length with a wingspan of 76 feet.

Despite its size, the YB-9 was agile and faster than most biplane fighters of its time, reaching a top speed of around 188 miles per hour.

The Y1B-9.
The Y1B-9.

Its impressive performance was partly due to the attention given to aerodynamics, which was particularly evident in its sleek, rounded lines and the internal storage of its bomb load.

Operational History

The YB-9, also known as the B-9 “Death Angel,” first took to the skies in 1931.

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However, it wasn’t until 1932 that the USAAC ordered a small batch of seven service test Y1B-9A aircraft.

These aircraft were used in several operational evaluations and exercises, the most notable being the 1934 Air Corps manoeuvres.

Despite its initial promise, the operational life of the YB-9 was relatively short. By the time of its deployment, more advanced bomber designs were on the drawing board.

The YB-9 and a P-26 Peashooter flying together.
The Y1B-9A and a P-26 Peashooter flying together.

Although the YB-9 was faster than any existing USAAC pursuit aircraft when it was introduced, its advantage was soon negated by rapidly evolving aircraft technology.

The YB-9 and its variants were retired from USAAC service by the end of 1934.

However, the experience and lessons learned from the YB-9’s design and operations greatly influenced the development of future bomber aircraft. Notably, its monoplane design and all-metal construction set a standard for subsequent bombers.

The YB-9 & Y1B-9

The Boeing YB-9 had a crew of five: a pilot, co-pilot, bombardier, and two gunners. It was armed with three .30-caliber machine guns: one in the nose, one in a dorsal turret, and one in a ventral position.

On the YB-9, the gunners operated three .30-caliber machine guns: one in a nose position, one in a dorsal (upper) turret, and one in a ventral (lower) position.

This setup provided 360-degree defensive coverage for the bomber, allowing it to ward off attacks from any direction.

It’s worth noting that the working conditions for gunners during this era were tough. The enclosed turrets on the YB-9 offered some protection from the elements, but the gunners were still exposed to high noise levels, extreme temperatures, and potential enemy fire.

The YB-9 had gun turrets that used Browning .30 cal machine guns.
The YB-9 had gun turrets that used Browning .30 cal machine guns.

Nevertheless, the role of the gunner was crucial for the survival of the aircraft and its crew during missions, and their contribution to the YB-9’s operations was indispensable.

The bomber’s bomb bay could carry up to 2,260 pounds of bombs and it was powered by its two Pratt & Whitney engines – the R1860 Hornet.

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The R-1690 Hornet was a 9-cylinder, single-row, air-cooled radial engine with a displacement of 1,690 cubic inches (about 27.7 liters).

This engine series saw extensive use in a variety of aircraft during the 1930s and gave the YB-9 a maximum speed of 188 mph, a cruising speed of 158 mph, and a range of approximately 630 miles.

A Pratt and Whitney Hornet engine.
A Pratt and Whitney Hornet engine.

The service ceiling, the maximum altitude the aircraft can fly, was about 21,210 feet.

The Y1B-9A was a refined version of the original YB-9 bomber.

The most significant change in the Y1B-9A was the replacement of the original Pratt & Whitney R-1860 Hornet B engines with the more powerful Wright R-1820-21 Cyclone engines, each delivering 700 horsepower. This change resulted in a higher top speed and better overall performance.

These powerful engines made the YB-9 faster than aircraft like the Curtiss P-6 Hawk, a mainstay of the United States Army Air Corps during the early 1930s.

A biplane design with a top speed of about 178 mph, the P-6 Hawk was renowned for its handling and manoeuvrability.

Physically, the Y1B-9A was similar to the initial YB-9 model, featuring an all-metal, monoplane design, retractable landing gear, and enclosed cockpits.

It carried a crew of five, which included a pilot, co-pilot, bombardier, and two gunners.

The Y1B-9A held an operational advantage over many of the biplane fighters of its era. However, this advantage was short-lived due to the rapid advancements in aircraft technology during the 1930s.

Though its service life was brief, the Boeing Y1B-9A, like its predecessor, contributed to the transition from biplane to monoplane designs in military aviation and influenced the development of future bombers.


The Boeing YB-9, despite its brief operational history, left an indelible mark on the evolution of military aviation. It was a symbol of a transformative period, a shift from the era of wooden biplanes to the age of all-metal monoplanes.

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Although the YB-9 was soon outclassed by newer aircraft designs, its pioneering innovations contributed significantly to the development of future bombers.

Today, as we marvel at the advanced bombers in our arsenals, it’s crucial to remember the role played by predecessors like the YB-9 in shaping modern aviation history.

It is not known what has happened to all of the airframes, however, it is known that older military aircraft were often repurposed, used for training or experimental purposes, or simply scrapped.

It is therefore plausible that the Y1B-9As shared a similar fate and YB-9 or Y1B-9A aircraft are known to exist today, suggesting that none were preserved.

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  • Crew: four
  • Length: 52 ft 0 in (15.85 m)
  • Wingspan: 76 ft 10 in (23.42 m)
  • Height: 12 ft 0 in (3.66 m)
  • Empty weight: 8,941 lb (4,056 kg)
  • Max takeoff weight: 14,320 lb (6,495 kg)
  • Powerplant: 2 × Pratt & Whitney R-1860-11 Hornet B radial engine, 600 hp (450 kW) each
  • Maximum speed: 188 mph (303 km/h, 163 kn) at 6,000 ft (1,800 m)
  • Cruise speed: 165 mph (266 km/h, 143 kn)
  • Range: 540 mi (870 km, 470 nmi)
  • Service ceiling: 20,750 ft (6,320 m)
  • Rate of climb: 900 ft/min (4.6 m/s)