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Airco DH.4

From Alfawiki
Airco
IndustryAerospace
Founded1912
FounderGeoffrey de Havilland
Headquarters
United Kingdom


"DH-4" redirects here. For the 1950s flying platform, see de Lackner HZ-1 Aerocycle.

Template:Infobox aircraft

The Airco DH.4 was a British two-seat biplane designed as a day bomber during the First World War. Created by Geoffrey de Havilland (hence the "DH" designation) for Airco, it was the first British light day-bomber capable of self-defense.

Conceived specifically for bombing operations as well as aerial reconnaissance, the DH.4 was initially intended to be powered by the new 160 hp (120 kW) Beardmore Halford Pullinger (BHP) engine. However, difficulties with this engine led to the use of various alternatives, with the 375 hp (280 kW) Rolls-Royce Eagle regarded as among the most effective powerplants. The aircraft’s maiden flight occurred in August 1916, and it entered service in France on 6 March 1917, less than a year later. Most DH.4s were produced as versatile two-seaters in the United States for American Expeditionary Forces in France, making it the only American-built aircraft to engage in combat during WWI.

After the Armistice on 11 November 1918, numerous DH.4s transitioned to civilian use, proving especially valuable as mail carriers. Modified versions of the DH-4 initiated some of Europe’s earliest commercial passenger flights. Surplus warplanes like the DH-4 played a significant role in forming new air forces worldwide. The U.S. Army subsequently had several manufacturers upgrade remaining DH.4s to the DH.4B standard, operating them into the early 1930s.

Origins

Geoffrey de Havilland designed the DH.4 as a lightweight two-seat combat aircraft intended for both day bombing and reconnaissance roles.[1] It was originally planned to be powered by the newly developed 160 hp (120 kW) Beardmore Halford Pullinger (BHP) engine. The DH.4 was developed alongside its competitor, the Bristol F.2 Fighter.[1] The prototype first took to the air in August 1916, equipped with a prototype 230 hp (170 kW) BHP engine.[2]

Early flight tests demonstrated favourable handling characteristics and performance.[3] The prototype underwent evaluation at the Central Flying School, which produced a positive assessment citing good stability, responsive controls, and relatively comfortable crew accommodations. During these trials, it achieved unprecedented climb times unmatched by previous aircraft.[3] Despite promising results from these flights, it became apparent that significant redesign would be necessary before the BHP engine could enter mass production.[3]

At the time of prototype testing, no finalized plans existed for large-scale manufacture of the BHP engine.[3] Meanwhile, another promising powerplant—the water-cooled inline Rolls-Royce Eagle—was nearing completion of its development phase.[1] According to Bruce, the Eagle’s configuration closely resembled that of the BHP engine, facilitating its adoption by de Havilland; this transition was further supported by endorsement from William Beardmore.[1] A second prototype powered by the Rolls-Royce Eagle conducted its first flight during summer 1916.[3]

Following encouraging performance evaluations, the Royal Flying Corps placed an initial order for production late in 1916.[4] Alongside RFC interest, considerable attention came from the Royal Navy.[5] The Admiralty commissioned two additional prototypes tailored to naval requirements for testing; however, it is doubtful that both were completed.[5] After successful trials of these prototypes, orders were placed to equip the Royal Naval Air Service with DH.4s.[5]

Production

File:EarlyDH4.jpg
An early production DH.4

In late 1916, the Royal Flying Corps placed an initial order for 50 DH.4 aircraft, each equipped with the 250 hp (190 kW) Eagle III engine.[6] Bruce notes that the selection of the Eagle engine for this first production series was anticipated by most experts.[4] These early production models closely resembled the second prototype, with the primary modification being the installation of armament: a single synchronized 0.303 in (7.7 mm) Vickers machine gun for the pilot and a 0.303 in (7.7 mm) Lewis gun mounted on a Scarff ring for the observer.[7]

Manufacturing of the DH.4 was not limited to Airco; several other firms contributed to production, including F.W. Berwick and Co, Glendower Aircraft Company, Palladium Autocars, Vulcan Motor and Engineering, and Westland Aircraft Works.[8] By the conclusion of production, Britain had completed 1,449 units out of 1,700 ordered for both the Royal Flying Corps and Royal Naval Air Service.[9] Additionally, in 1926, Belgium’s SABCA manufactured 15 more DH.4s.[10][8]

Throughout production, numerous design enhancements were incorporated into the DH.4.[5] Over time, aircraft were fitted with progressively more powerful Eagle engines, culminating in the 375 hp (280 kW) Eagle VIII powering most frontline DH.4s by late 1917. Nonetheless, this upgrade process faced significant delays due to a severe shortage of Rolls-Royce aero engines—particularly the Eagle model—by January 1917; Bruce attributes part of this scarcity to prolonged decision-making by the Air Board.[5]

To address the Eagle engine's limited supply, extensive trials with alternative powerplants were undertaken. Various engines such as the BHP (230 hp (170 kW)), Royal Aircraft Factory’s RAF3A (200 hp (150 kW)), Siddeley Puma (230 hp (170 kW)), and Fiat (260 hp (190 kW)) were installed in production DH.4s with mixed results.[6] Despite these alternatives, none matched the performance of the Eagle engine, which continued to be preferred even amid ongoing shortages.[11]

American versions

File:Assembling liberty planes at Romorantin (cropped).jpg
American DH.4 aircraft being assembled in France during World War One

When the United States entered World War I on April 6, 1917, its aviation branch within the U.S. Signal Corps lacked combat-ready aircraft.[12] Nevertheless, there was significant enthusiasm and effort to rectify this deficiency by mobilizing American industry to produce modern combat planes. Since no suitable domestic designs existed at that time, a technical delegation known as the Bolling Commission was sent to Europe to identify leading combat aircraft and arrange for their manufacture in America.[12]

Following their evaluation, the Bolling Commission selected several aircraft types for American production: the DH.4 alongside the Bristol F.2 Fighter, Royal Aircraft Factory S.E.5, and French SPAD S.XIII.[12] On July 27, 1917, one DH.4 was shipped to the United States as a reference model; however, American-built DH.4s did not begin rolling off assembly lines until 1918.[13] Multiple manufacturers—including Boeing Airplane Corporation, Dayton-Wright Company, Fisher Body Corporation, and Standard Aircraft Corporation—produced this Americanized DH.4 variant featuring over a thousand modifications compared to its British counterpart to suit U.S. military requirements.[14] The United States ordered approximately 9,500 DH.4s from these producers; about 1,885 were delivered to France during wartime service. The American models employed the new Liberty engine, which proved effective as a powerplant for the DH.4 and was later adopted by British forces for their DH.9A version.[15][16]

Postwar contracts saw companies like Boeing rebuild surplus DH.4s to an upgraded standard known as the DH.4B; Boeing internally designated these as Model 16. Between March and July 1920 alone, Boeing delivered 111 refurbished aircraft; approximately half were returned three years later for additional overhauls.[17][18]

In 1923, Boeing received an order from the Army for a new DH.4 variant distinguished by a fabric-covered steel tube fuselage replacing the original plywood structure.[19] These three prototypes were designated DH.4M-1 (M signifying modernized) and entered production alongside a similar model—the DH.4M-2—developed by Atlantic Aircraft. Out of 163 DH.4M-1 units produced for the Army, twenty-two were modified into dual-control trainers (DH.4M-1T), with several others converted into target tugs (DH.4M-1K). Additionally, thirty aircraft initially ordered by the Army were reassigned to Navy Marine Corps service under designations O2B-1 for standard models and O2B-2 for those equipped for night and cross-country missions.[20]

Design

File:"Strength tests on DH-4 airplane wing ribs Project-L-225-2" from- Forest Products Laboratory for Research Work during the war. Illustrating the development in designing a wing rib for De Haviland airplane - NARA - 17341228 (cropped).jpg
Strength evaluations on various DH-4 wing ribs during World War I

The Airco DH.4 featured a conventional tractor configuration with a two-bay biplane layout, constructed entirely from wood.[1] Traditional materials were used throughout its build. The forward fuselage and the underside of the tail section were covered with a 3mm plywood skin, resulting in a fuselage that was both robust and lightweight. This design allowed cross-bracing to be limited to the four bays immediately behind the rear cockpit.[1] The aircraft's nose was notably longer than necessary because its cowling was initially designed for the Beardmore Halford Pullinger (BHP) engine, but production models instead utilized the Rolls-Royce Eagle engine.[1]

Various engines powered the DH.4, including the Eagle, BHP, American Liberty L-12, Royal Aircraft Factory RAF3A, Siddeley Puma, and Fiat units.[1] Regardless of the engine type, all drove a four-bladed propeller mounted at the front of the aircraft. Engine cooling was managed through an oval radiator, while exhaust gases were expelled via a port-side manifold above the upper wing.[1] A distinctive modification appeared on some DH.4s where the engine was inverted to better fit the relatively tall Ricardo-Halford-Armstrong (RHA) supercharged engine, preventing obstruction of the pilot’s forward visibility.[11]

The crew consisted of two members seated in widely spaced cockpits with the fuel tank situated between them.[6] This arrangement offered excellent visibility for both pilot and observer but hindered communication, especially during combat where the speaking tube connecting the cockpits proved only marginally effective.[21][4] In most American-built versions, the positions of the pilot’s seat and fuel tank were reversed; aviation historian Peter M. Bowers attributes this alteration to enhanced pilot safety in crashes and improved communication with the observer.[22]

Armament on the DH.4 included one forward-firing synchronized Vickers machine gun and one or two .303-inch Lewis guns mounted on a Scarff ring operated by the observer. The aircraft could carry up to 460 pounds of bombs on external racks.[21] Throughout its production run, modifications were made to improve armament ergonomics, such as adjustments to the observer’s Lewis gun setup and adding an extra Vickers gun.[11] Two DH.4s were experimentally equipped with COW 37 mm cannons; however, firing tests did not occur before World War I ended.[8] Typically, all weaponry was removed from DH.4s converted for civilian use or those sold as surplus after the war.

Among its more complex variants was a seaplane version of the DH.4.[8] This model was fitted with large floats reportedly inspired by those used on the German Hansa-Brandenburg W.29 seaplane. Although no seaplane DH.4 entered operational service due to competition from other aircraft types, several were built for trials at Felixstowe and successfully flown.[8]

British military service

The DH.4 was introduced into the Royal Flying Corps (RFC) in January 1917, initially deployed by No. 55 Squadron. Over the course of the year, additional squadrons were outfitted with this model to enhance the RFC's bombing capabilities; two more squadrons received the aircraft in May, and by year-end a total of six squadrons operated the type. The pace of adoption accelerated in late 1917 as the RFC sought to conduct retaliatory bombing missions against Germany following attacks on British soil. Although Russia had placed an early order for 50 DH.4s in September 1917, an agreement between the Russian and British governments postponed deliveries to Russia, redirecting those aircraft to RFC units stationed in France.

In addition to the RFC, the Royal Naval Air Service (RNAS) also operated the DH.4. In spring 1917, No. 2 Squadron became the first RNAS unit to receive these aircraft. The RNAS deployed their DH.4s over both France and the Aegean front in Italy. Primarily, the DH.4 served coastal patrol duties within RNAS operations. Notably, a flight piloted by Major Egbert Cadbury with Captain Robert Leckie as gunner successfully downed Zeppelin L70 on 5 August 1918. Furthermore, a formation of four RNAS DH.4s was collectively credited with sinking the German submarine UB 12 on 19 August 1918.

Regarded as one of World War I’s premier single-engine bombers, the DH.4 earned widespread acclaim for its effectiveness. Despite carrying full bomb loads, its reliability and strong performance made it popular among aircrew. The Airco DH.4 was straightforward to pilot and, particularly when powered by the Rolls-Royce Eagle engine, it delivered superior speed and altitude capabilities that often rendered it immune to interception by German fighters. This capability frequently eliminated the need for fighter escorts during missions—a concept that influenced later designs such as de Havilland’s Second World War Mosquito.

One notable design limitation was the considerable gap between pilot and observer caused by the large central fuel tank, which hindered crew communication during combat engagements with enemy fighters. This fuel tank placement also sparked safety concerns, especially within American service circles, due to perceived fire risks. Nonetheless, many contemporary aircraft were vulnerable to inflight fires; although sometimes nicknamed the "Flaming Coffin," records indicate that only eight out of 33 DH-4 losses to enemy action involved fire—comparable with other aircraft of that era. The hazard was mitigated when a pressurized fuel system was replaced by wind-driven fuel pumps late in 1917, although American-built versions initially did not adopt this change. By contrast, the subsequent Airco DH.9 design relocated the fuel tank between pilot and engine, bringing crew members closer but ultimately proving inferior to the DH.4 in most respects.

Despite its success, RFC numbers of DH.4s began to decline from spring 1918 due to engine shortages; production shifted toward the DH.9 model, which failed to meet expectations compared with its predecessor. It was only with the introduction of the improved Airco DH.9A powered by the American Liberty engine that a satisfactory replacement for the DH.4 emerged.

When the Independent Air Force was established in June 1918 to conduct strategic bombing against German targets, DH.4s from 55 Squadron were integral to daylight raid operations. This squadron developed tactics involving wedge formations flying under a leader’s command while relying on collective defensive firepower to deter enemy fighter attacks. Despite sustaining heavy casualties, 55 Squadron remained operational throughout and was unique among day-bombing squadrons in not having to pause activities due to personnel losses.

Following the Armistice, the RAF created No. 2 Communication Squadron, which utilized DH.4s for transporting key delegates to and from the Paris Peace Conference. Several aircraft were modified with enclosed cabins accommodating two passengers at Bonar Law’s request; one such plane saw extensive use by Prime Minister David Lloyd George and earned recognition as possibly the first aircraft widely employed by a political leader. These modified versions were designated DH.4A, with at least seven conversions for RAF use and nine additional adaptations for civilian operations.

United States military service

When the United States Army Air Service entered World War I, it did not possess any aircraft appropriate for frontline combat. Consequently, it acquired several aircraft models from British and French manufacturers, including the DH.4. Known as the DH-4 in U.S. service, production was primarily handled by Dayton-Wright and Fisher Body starting in 1918. The first domestically produced DH-4 was delivered to France in May 1918, with combat missions beginning by August of the same year. Powered by a 400 hp (300 kW) Liberty L-12 engine, the DH-4 was armed with two synchronized .30 in (7.62 mm) Marlin-Rockwell M1917 machine guns mounted in the nose and two .30 in (7.62 mm) Lewis guns operated from the rear cockpit. It could carry up to 322 lb (146 kg) of bombs and was equipped to use various radios such as the SCR-68 for artillery spotting tasks. Although its heavier Liberty engine resulted in reduced performance compared to the Rolls-Royce powered original, the aircraft earned the nickname "Liberty Plane" and became the standard two-seat general-purpose aircraft for the U.S. Army Air Service, enjoying considerable favor among its crews.

File:A Concise History of the U.S. Air Force Page 06-1.jpg
A formation of DH-4s in flight

Among American aviators, crews flying the DH-4 received four out of six Medal of Honor awards during the conflict. Posthumous honors were bestowed upon First Lieutenant Harold Ernest Goettler and Second Lieutenant Erwin R. Bleckley, who lost their lives on 12 October 1918 while attempting to deliver supplies to the isolated Lost Battalion of the 77th Division, surrounded by German forces during the Meuse-Argonne Offensive. Meanwhile, Second Lieutenant Ralph Talbot and Gunnery Sergeant Robert G. Robinson of the United States Marine Corps earned Medals of Honor for successfully defending their aircraft against attacks by 12 German fighters during a bombing mission over Belgium on 8 October 1918. By the end of 1918, thirteen U.S. squadrons were operating DH-4s.

After World War I concluded, a surplus of DH-4s remained in American inventory, including the enhanced DH-4B variant; however, none had been shipped overseas to France. Given this situation, authorities decided against transporting aircraft back across the Atlantic. Instead, remaining planes in France along with outdated observation and training aircraft were destroyed in what became known as the "Billion Dollar Bonfire." Due to constrained budgets for development and procurement of new aircraft, existing DH-4s continued to constitute a significant portion of American air power for several years across numerous roles, with up to 60 different variants produced. The DH-4 also played a key role in experimental aviation activities such as serving as engine test platforms and being fitted with new wing designs. Notably, it was involved in pioneering trials of air-to-air refueling on 27 June 1923 and achieved an endurance record by remaining airborne for 37 hours and 15 minutes between 27–28 August while being refueled sixteen times, setting sixteen new world records for distance, speed, and duration during that flight. The DH-4 remained operational within the United States Army Air Corps, successor to the Army Air Service, until 1932.

The United States Navy and United States Marine Corps also operated large numbers of DH-4s both during World War I and afterward. During wartime, they received 51 DH-4s followed by an additional 172 DH-4B and DH-4B-1 models postwar, plus 30 DH-4M-1 aircraft featuring welded steel-tube fuselages (later redesignated O2B) beginning in 1925. The Marine Corps continued using these planes until 1929, employing them notably in operations against insurgents in Nicaragua in 1927 where they conducted what are considered the first dive-bombing attacks executed by U.S. military forces. Some DH-4M-1s were converted by the Navy into rudimentary air ambulances capable of transporting a single stretcher patient within an enclosed compartment located behind the pilot’s seat.

Civil applications

File:DH-4 airmail.jpg
Robertson Aircraft Corp. operated DH-4 mailplane (CAM 2) 1926 at the Historic Aircraft Restoration Museum

After the conclusion of the First World War, numerous DH.4 and DH.4A aircraft were employed to provide scheduled passenger flights across Europe by carriers such as Aircraft Transport and Travel, Handley Page Transport, and the Belgian airline SNETA. On 25 August 1919, Aircraft Transport and Travel's G-EAJC conducted the inaugural British commercial passenger flight from Hounslow Heath Aerodrome to Paris Le Bourget, transporting a journalist from the Evening Standard along with newspapers and other cargo. These aircraft remained in service with Aircraft Transport and Travel until its closure in 1920, whereas Handley Page Transport and SNETA continued operating the DH.4 until 1921. Additionally, one DH.4 was utilized by Instone Air Line until its incorporation into Imperial Airways in 1924.

File:DeHavilland Biplane stamp 24c 1923 issue.JPG
In 1923, the U.S. Post Office issued a postage stamp depicting the DeHavilland Biplane used for airmail delivery

On September 4, 1922, Jimmy Doolittle completed the first cross-country flight piloting a de Havilland DH-4 outfitted with early navigation tools, traveling from Pablo Beach (present-day Jacksonville Beach), Florida, to Rockwell Field, San Diego, California, in 21 hours and 19 minutes, with a single refueling stop at Kelly Field.

The Australian carrier QANTAS also employed the DH.4 for its initial airmail service in 1922. Twelve DH.4 aircraft included in the Imperial Gift to Canada were assigned to forestry patrols and aerial surveys, detecting hundreds of forest fires and thereby protecting timber resources valued at millions of dollars; these planes remained operational until their final retirement in 1927.

The U.S. Post Office adopted the DH-4 for airmail transport as well. In 1918, it procured 100 units from military surplus and converted them into safer configurations known as DH.4B models. By 1919, the U.S. Post Office standardized the DH-4B, modifying it to be flown from the rear cockpit while replacing the forward cockpit with a watertight mail compartment capable of carrying 400 lb (180 kg) of mail. Subsequent alterations included updated landing gear and an enlarged rudder. The DH-4 was instrumental in establishing a transcontinental airmail route spanning approximately 2,680 mi (4,310 km) between San Francisco and New York, incorporating night flights that commenced on 21 August 1924. The aircraft continued serving postal routes until 1927, when private contractors assumed responsibility for these services.

Surplus war-era DH-4s were widely accessible at low cost, fostering growth in "utility aviation" sectors such as aerial surveying, commercial photography, law enforcement operations, agricultural tasks, and other practical uses.[23]

Variants

File:Airco DH-4.jpg
DH-4 flying high above the clouds over France
File:Wright Radial Engine in a De Havilland DH-4B airplane (00910460 163).jpg
Wright Radial Engine (R-1) installed in a De Havilland DH-4B frame

British variants

  • DH.4 : Two-seat biplane designed for daytime bombing missions.
  • DH.4A : Transport adaptation produced in the United Kingdom, accommodating two passengers in a glazed cabin located behind the pilot.
  • DH.4R : Single-seat racing model powered by a 450 hp (340 kW) Napier Lion engine.

Soviet variants

American variants

  • DH-4 : Two-seat day bomber biplane constructed in the United States.
  • DH-4A : Civilian version produced domestically.
  • DH-4B : Modified Liberty engine-powered DH-4 for the U.S. Air Service, featuring relocation of the pilot’s cockpit behind the fuel tank, adjacent to the observer.
    • DH-4B-1 : Version with increased fuel capacity of 110 US gal (420 L; 92 imp gal).
    • DH-4B-2 : Trainer variant.
    • DH-4B-3 : Equipped with a larger 135 US gal (510 L; 112 imp gal) fuel tank.
    • DH-4B-4 : Civilian model.
    • DH-4B-5 : Experimental civilian conversion featuring an enclosed cabin.
  • DH-4BD : Cropdusting adaptation of the DH-4B.
  • DH-4BG : Outfitted with smokescreen generators.
  • DH-4BK : Designed for night operations.
  • DH-4BM : Single-seat communication version.
    • DH-4BM-1 and DH-4BM-2 : Dual-control versions of the BM model.
  • DH-4-BP : Experimental photo reconnaissance aircraft.
    • DH-4-BP-1 : BP variant adapted for survey missions.
  • DH-4BS : Test platform for supercharged Liberty engines.
  • DH-4BT : Dual-control trainer model.
  • DH-4BW : Testbed for Wright H engine trials.
  • DH-4C : Powered by a 300 hp (220 kW) Packard engine.
  • DH-4L : Civilian configuration.
  • DH-4M : Reconstructed DH-4 featuring a steel tube fuselage.
  • DH-4Amb : Ambulance conversion.
  • DH-4M-1 : Postwar redesign by Boeing (Model 16), incorporating a new fuselage; designated as O2B-1 by the Navy.
    • DH-4M-1T : Trainer variant with dual controls based on DH-4M.
    • DH-4M-1K : Converted into a target tug.
    • O2B-2 : Modified for cross-country and night flying duties for Navy use.
  • DH-4M-2 : Postwar model developed by Atlantic Aircraft Corporation.
  • L.W.F. J-2 (also called Twin DH) : Twin-engine extended-range development of the DH-4, powered by two 200 hp (150 kW) Hall-Scott Liberty L-6 engines, featuring a wingspan of 52 ft 6 in (16.00 m); 20 units supplied to the U.S. Post Office and 10 to the U.S. Army.
XCO-7
(Boeing Model 42) Two-seat observation aircraft equipped with Boeing-designed wings, an enlarged tailplane, and split landing gear.
XCO-8
Designation assigned to an Atlantic DH.4M-2 fitted with Loening COA-1 wings and powered by a Liberty 12A engine.

Civil operators

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Military operators

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File:Canadian Red Ensign (1921–1957).svg Canada
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File:Flag of Greece (1822-1978).svg Greece
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  • The New Zealand Permanent Air Force operated two units from 1919 through 1929, utilizing the DH.4 as an advanced trainer. Notably, it was the first aircraft to fly over Mount Cook on 8 September 1920 and set a New Zealand altitude record of 21,000 ft (6,400 m) on 27 November 1919.
File:Red Ensign of South Africa (1912-1951).svg South Africa
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Spain Kingdom of Spain
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File:Flag of the United States (1912-1959).svg United States

Surviving aircraft

File:Airco DH-4 NMUSAF.jpg
The DH-4B exhibited at the National Museum of the United States Air Force
File:Friends of Jenny DH.4 side view.jpg
Friends of Jenny DH.4, photographed in 2018

DH-4:

DH-4B:

DH-4M-1:

DH-4M-2A:

Specifications (DH.4 – Rolls-Royce Eagle VIII Engine)

Template:Aircraft specs

See also

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Notes

Citations

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 Bruce, 1966, p.3
  2. ↑ Jackson, 1987, p.53
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Bruce, 1966, p.4
  4. ↑ 4.0 4.1 4.2 Cite error: Invalid <ref> tag; no text was provided for refs named BruceP3-4
  5. ↑ 5.0 5.1 5.2 5.3 5.4 Bruce, 1966, p.5
  6. ↑ 6.0 6.1 6.2 Cite error: Invalid <ref> tag; no text was provided for refs named Mason
  7. ↑ Bruce, 1966, pp.4–5
  8. ↑ 8.0 8.1 8.2 8.3 8.4 Cite error: Invalid <ref> tag; no text was provided for refs named BruceP10
  9. ↑ Jackson, 1987, p.54
  10. ↑ Jackson, 1987, p.60
  11. ↑ 11.0 11.1 11.2 Bruce, 1966, pp.5–8
  12. ↑ 12.0 12.1 12.2 Bowers, 1966, p.3
  13. ↑ Bowers, 1966, pp.3, 10
  14. ↑ Bowers, 1966, pp.3–4
  15. ↑ Jackson, 1987, p.58
  16. ↑ Bowers, 1966, pp.6–7
  17. ↑ Bowers, 1989, p.67
  18. ↑ Bowers, 1966, pp.7–8
  19. ↑ Bowers, 1966, p.9
  20. ↑ Bowers, 1989, p.70
  21. ↑ 21.0 21.1 Cite error: Invalid <ref> tag; no text was provided for refs named BruceP507
  22. ↑ Cite error: Invalid <ref> tag; no text was provided for refs named BowersP7
  23. ↑ "General Aviation,", in "History of Flight," Britannica, retrieved May 29, 2021
  24. ↑ Klaus, Erich. "Nicaragua Air Force Aircraft Types: de Havilland (Airco) DH.-4B." Archived 27 May 2008 at the Wayback Machine Aeroflight, 1 June 2003. Retrieved: 10 May 2008.
  25. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  26. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  27. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  28. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  29. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  30. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  31. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  32. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  33. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  34. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  35. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  36. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  37. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  38. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  39. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  40. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  41. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  42. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  43. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  44. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
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  46. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  47. ↑ Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).

Bibliography

  • Angelucci, Enzo, ed. World Encyclopedia of Military Aircraft. London: Jane's, 1991. ISBN 0-7106-0148-4.
  • Bruce, J.M. "The De Havilland D.H.4." Flight, 17 October 1952, pp. 506–510.
  • Bruce, J.M. The de Havilland D.H.4. (Aircraft in Profile number 26). London: Profile Publications, 1966. No ISBN.
  • Bowers, Peter M. Boeing Aircraft since 1916. London: Putnam, Second edition, 1989. ISBN 0-85177-804-6.
  • Bowers, Peter M. The American DH.4 (Aircraft in Profile number 97). London: Profile Publications, 1966. No ISBN.
  • Jackson, A.J. British Civil Aircraft since 1919: Volume 2. London: Putnam, Second edition, 1973. ISBN 0-370-10010-7.
  • Jackson, A.J. De Havilland Aircraft since 1909. London: Putnam, Third edition, 1987. ISBN 0-85177-802-X.
  • Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  • Mason, Francis K. The British Bomber since 1914. London: Putnam Aeronautical Books, 1994. ISBN 0-85177-861-5.
  • Maurer, Maurer, ed. The U.S. Air Service in World War I: Volume IV Postwar Review. Washington, D.C.: The Office of Air Force History Headquarters USAF, 1979.
  • Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
  • Sturtivant, Ray and Gordon Page. The D.H.4/D.H.9 File. Tonbridge, Kent, UK: Air-Britain (Historians) Ltd., 2000. ISBN 0-85130-274-2.
  • Swanborough, F.G. and Peter M. Bowers. United States Military Aircraft since 1909. London: Putnam, 1963.
  • Swanborough Gordon and Peter M. Bowers. United States Naval Aircraft since 1911. London: Putnam, Second edition, 1976. ISBN 0-370-10054-9.
  • Thetford, Owen. British Naval Aircraft since 1912. London: Putnam, Fourth edition, 1978. ISBN 0-370-30021-1.
  • Thomas, Andrew. "In the Footsteps of Daedulus: Early Greek Naval Aviation". Air Enthusiast, No. 94, July–August 2001, pp. 8–9. Template:ISSN
  • United States Air Force Museum Guidebook. Wright-Patterson AFB, Ohio: Air Force Museum Foundation, 1975.
  • Lua error in Module:Citation/CS1/Configuration at line 2123: attempt to index field '?' (a nil value).
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External links

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