| Airco DH.4 | |
|---|---|
 A Canadian DH.4 registere G-CYDK parked. | |
| General information | |
| Type | Light bomber / General purpose |
| Manufacturer | Airco |
| Built by | Boeing Airplane Corporation Dayton-Wright Company Fisher Body Standard Aircraft Corporation |
| Status | Retired |
| Primary users | Royal Flying Corps |
| Number built | 6,295, of which 4,846 were built in the United States.[1][2] |
| History | |
| Introduction date | March 1917 |
| First flight | August 1916 |
| Retired | 1932 (United States Army Air Service) |
| Developed into | Airco DH.9 Airco DH.9A Dayton-Wright Cabin Cruiser |
TheAirco DH.4 is a British two-seatbiplaneday bomber of theFirst World War. It was designed byGeoffrey de Havilland (hence "DH") forAirco, and was the first British two-seat light day-bomber capable of defending itself.
It wasdesigned and developed specifically as a bomber, as well asaerial reconnaissance missions. The DH.4 was to have been powered by the new 160 hp (120 kW)Beardmore Halford Pullinger (BHP) engine, but problems with that resulted in numerous other engines being used, perhaps the best of which was the 375 hp (280 kW)Rolls-Royce Eagle engine. The DH.4 first flew in August 1916 and it entered operational service in France on 6 March 1917 less than a year later. The majority were manufactured as general purpose two-seaters in theUnited States for the American expeditionary forces in France, becoming the only American made plane to see combat in WW1.
Following theArmistice of 11 November 1918, many DH.4s were sold to civil operators where it was found to be particularly useful as amailplane. Early commercial passenger airplane service in Europe was initiated with modified variants of the DH-4. War-surplus DH-4s became key aircraft in newly emerging air forces throughout the world. The U.S. Army later had several companies re-manufacture its remaining DH.4s to DH.4B standard and they operated the type into the early 1930s.
The DH.4 was designed by Geoffrey de Havilland as a light two-seat combat aircraft, intended to perform bothday bomber andaerial reconnaissance missions.[3] The intention was for it to be powered by the newly developed 160 hp (120 kW)Beardmore Halford Pullinger (BHP) engine. The DH.4 was developed in parallel to the rivalBristol Fighter.[3] During August 1916, the prototype DH.4 made its first flight, powered by a prototype 230 hp (170 kW) BHP engine.[4]
Initial flight tests revealed it to have favourable handling and performance.[5] TheCentral Flying School (CFS) conducted early evaluation flights using the prototype, leading to it producing a favourable report on the aircraft, observing good stability in flight, light flying controls and its relatively comfortable crew positions. During its flights with the CFS, it was able to attain previously unheard-of time-to-altitude figures, unmatched by any of its predecessors.[5] While flying trials with the prototype had been producing promising results, it soon became clear that the BHP engine would require a major redesign prior to entering production.[5]
Even by the time of flying trials with the first prototype, there had been no finalised plans for quantity production of the BHP engine.[5] Coincidentally, another suitable and promising aeroengine, the water-cooledRolls-Royce Eagle in-line engine, was approaching the end of its development process.[3] According to Bruce, the Eagle shared the same basic configuration as the BHP engine, which greatly aided in its adoption by de Havilland, as did the engine's endorsement byWilliam Beardmore. During the summer of 1916, a second prototype, equipped with the Rolls-Royce engine, conducted its first flight.[5]
In response to its favourable performance, theRoyal Flying Corps (RFC) decided to place an initial order for the type during late 1916.[6] Separately to the RFC's interactions with the DH.4, it had received substantial interest from theRoyal Navy as well.[7] TheAdmiralty decided to order a further pair of prototypes, configured to suit the service's own requirements, for evaluation purposes; however, according to Bruce, it is unlikely that the second of these was ever constructed. Following trials with the first of these prototypes, orders were placed for the production of DH.4s to equip theRoyal Naval Air Service.[7]
During late 1916, the first order for 50 DH.4s, powered by 250 hp (190 kW) Eagle III engines, was received from the RFC.[8] According to Bruce, it was not a surprise to most observers that the Eagle had been selected to power the first batch of production DH.4s.[6] The initial production aircraft were largely identical to the second prototype, the main difference being the adoption of armament, which included a single synchronised 0.303 in (7.7 mm)Vickers machine gun for the pilot, while the observer was provided with a 0.303 in (7.7 mm)Lewis gun mounted upon aScarff ring.[9]
Production of the DH.4 was performed by a variety of companies beyond Airco themselves; these included F.W. Berwick and Co, Glendower Aircraft Company, Palladium Autocars, Vulcan Motor and Engineering, and theWestland Aircraft Works.[10] By the end of production, a total of 1,449 aircraft (from orders for 1,700 aircraft) were constructed in Britain for theRoyal Flying Corps (RFC) and theRoyal Naval Air Service (RNAS).[11] Overseas,SABCA ofBelgium produced a further 15 DH.4s during 1926.[12][10]
As production progressed, various changes and improvements to the design were introduced upon the DH.4.[7] As time went on, production DH.4s were fitted with Eagle engines of increasing power, ending with the 375 hp (280 kW) Eagle VIII, which powered the majority of frontline DH.4s by the end of 1917. However, this transition was greatly hindered as by January 1917, it had become clear that there was a chronic shortage of Rolls-Royce aero engines, and of the Eagle in particular; it has been claimed by Bruce that this shortfall was partially the result of protracted decision-making on the part of the Air Board.[7]
In response to the limited availability of the Eagle, extensive investigations into the use of alternative engines for the DH.4 were conducted. This resulted in aircraft being outfitted with a diverse range of engines; these included the BHP (230 hp (170 kW), theRoyal Aircraft FactoryRAF3A (200 hp (150 kW)), theSiddeley Puma (230 hp (170 kW)) and the 260 hp (190 kW)Fiat, all of which were used to power production aircraft, with varying degrees of success.[8] None of these engines proved to be capable of matching the performance of the Eagle engine, which remained the preferred options despite the persistent supply constraints.[13]
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At the time of entry of theUnited States into the First World War on 6 April 1917, the aviation section of theU.S. Signal Corps was unprepared, not being equipped with any aircraft suitable for combat.[14] However, considerable optimism and energy was put into addressing this identified need, leading to the mobilization of American industry to set about the production of contemporary combat aircraft. As there were no suitable aircraft domestically, a technical commission, known as the Bolling Commission, was dispatched to Europe to seek out the best available combat aircraft and to make arrangements to enable their production to be established in the United States.[14]As a result of the efforts of the Bolling Commission, the DH.4, along with theBristol F.2 Fighter, theRoyal Aircraft Factory S.E.5, and FrenchSPAD S.XIII were selected.[14] On 27 July 1917, a single DH.4 was sent to the United States as a pattern aircraft. It was not until 1918 that the first American-built DH.4s came off the production line.[15] Several different manufacturers, including theBoeing Airplane Corporation,Dayton-Wright Company, theFisher Body Corporation, and theStandard Aircraft Corporation produced this Americanized variant of the DH.4, featuring over 1,000 modifications from the original British design, to equip the American air services.[16] A total of 9,500 DH.4s were ordered from American manufacturers, of which 1,885 actually reached France during the war. In American production, the newLiberty engine, which had proved suitable as a DH.4 power plant, was adopted. The Liberty was also eventually adopted by the British to power theDH.9A variant of the type.[1][17]
After the war, a number of firms, most significant of these beingBoeing, were contracted by the U.S. Army to remanufacture surplus DH.4s to the improved DH.4B standard. Internally referred to by Boeing as theModel 16, deliveries of 111 aircraft from this manufacturer took place between March and July 1920; reportedly, roughly 50 of these were returned for further refurbishments three years later.[18][19]
During 1923, the Army placed an order for a new DH.4 variant from Boeing, distinguished by a fuselage of fabric-covered steel tube in place of the original plywood structure.[20] These three prototypes were designatedDH.4M-1 (M for modernized) and were ordered into production alongside the generally similarDH.4M-2 developed byAtlantic Aircraft. A total of 22 of the 163 DH.4M-1s were converted by the Army into dual-control trainers (DH.4M-1T) and a few more into target tugs (DH.4M-1K). Thirty of the aircraft ordered by the Army were diverted to the Navy for Marine Corps use, these designatedO2B-1 for the base model, andO2B-2 for aircraft equipped for night andcross-country flying.[21]
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The Airco DH.4 was a conventional tractortwo bay biplane of all-wooden construction.[3] It was entirely built of traditional materials. The forward fuselage section and the underside of the tail area was covered by a 3mmplywood skin; this construction led to the fuselage being both strong and lightweight, heavily contributing to cross-bracing only being used for the four bays directly behind the rear cockpit.[3] The nose of the aircraft was considerably longer than necessary, the cowling having been originally designed to accommodate theBeardmore Halford Pullinger (BHP) engine, rather than theRolls-Royce Eagle that was adopted for production instead.[3]
The DH.4 was powered by a variety of engines, including the Eagle, the BHP, the AmericanLiberty,Royal Aircraft FactoryRAF3A, theSiddeley Puma and theFiat.[3] Regardless of the engine used, it drove a four-bladedpropeller mounted upon the nose. Cooling for the engine was provided via an oval-shaped radiator, while a port-mounted exhaust manifold discarded waste emissions above the upper wing.[3] An unusual modification featuring on a small proportion of production DH.4s was the inversion of the engine, a design change that had been implemented in order to better accommodate the relatively-tall Ricardo-Halford-Armstrong (RHA)supercharged engine, which would otherwise unduly obstruct the pilot's forward field of view.[13]
The DH.4 was operated by a crew of two, who were accommodated in widely spaced cockpits, between which the fuel tank was positioned.[8] While the crew arrangement provided good fields of view for both the pilot and observer; however, it had the noticeable downside of causing communication problems between the two crew members, particularly during combat situation, where thespeaking tube that linked the two cockpits was of only limited use.[22][6] On the majority of American-built aircraft, the pilot's seating and fuel tank arrangement were switched around; aviation author Peter M Bowers credits this change with improving the pilot's safety in the event of a crash, as well as allowing for better communication with the observer.[23]
The DH.4 was armed with a single forward-firing synchronisedVickers machine gun along with either one or two .303 in (7.7 mm)Lewis guns fitted on aScarff ring fired by the observer. In terms of bomb load, it accommodate a maximum payload of 460 lb (210 kg), which could be mounted upon external racks.[22] Throughout the type's production life, a number of alterations to the armaments, such as the ergonomics of the observer's Lewis gun and the installation of an additional Vickers gun, were implemented.[13] A pair of DH.4s were outfitted withCOW 37 mm guns for experimental purposes, but the war came to a close prior to firing trials being conducted.[10] All armaments would typically be removed from those DH.4s that were used by civil operators, including ex-military aircraft that were sold on in great numbers following the end of the Great War.
One of the more elaborate modifications of the DH.4 was the adaptation of the type as a seaplane.[10] It was furnished with largefloats, which were allegedly based upon the design of those used upon the GermanHansa-Brandenburg W.29 seaplane. According to Bruce, while no such aircraft entered into operational service as a result of competition from other aircraft to perform the role, a number of DH.4 seaplanes were produced for trial purposes atFelixstowe and were successfully flown.[10]
The DH.4 entered service with the RFC in January 1917, first being used byNo. 55 Squadron.[8] More squadrons were equipped with the type to increase the bombing capacity of the RFC, with two squadrons re-equipping in May, and a total of six squadrons by the end of the year.[8][24] During late 1917, the uptake of the type by the RFC was accelerated due to a desire to launch retaliatory bombing raids upon Germany following such attacks having been conducted against the British mainland. WhileRussia had been an early customer for the DH.4, having ordered 50 of the type in September 1917, the Russian and British governments subsequently agreed to delay the former's deliveries, instead diverting those aircraft to RFC squadrons in France.[25]
As well as the RFC, the RNAS also used the DH.4. During the spring of 1917,No. 2 Squadron became the first unit of the service to receive examples of the type.[24] The RNAS flew their DH.4s over bothFrance and overItaly, specifically theAegean front in the latter case.[8] The DH.4 was typically used to conduct coastal patrols by the RNAS. One such flight, crewed by the pilotMajorEgbert Cadbury andCaptainRobert Leckie (later Air Vice-Marshal) as gunner, shot downZeppelinL70 on 5 August 1918.[26] In another incident, a group of four RNAS DH.4s were jointly credited with the sinking of the GermanU-boatUB 12 on 19 August 1918.[26][27]
The DH.4 proved a huge success and was often considered the best single-engined bomber of World War I.[Note 1] Even when fully loaded with bombs, with its reliability and impressive performance, the type proved highly popular with its crews. The Airco DH.4 was easy to fly, and especially when fitted with the Rolls-Royce Eagle engine, its speed and altitude performance gave it a good deal of invulnerability to German fighter interception,[28] so that the DH.4 often did not require a fighter escort on missions, a concept furthered byde Havilland in the laterMosquito of the Second World War.
A drawback of the design was the distance between pilot and observer, as they were separated by the large main fuel tank. This made communication between the crew members difficult, especially in combat with enemy fighters.[29] There was also some controversy (especially in American service) that this placement of the fuel tank was inherently unsafe.[30][31] In fact, most contemporary aircraft were prone to catching fire in the air.[Note 2] The fire hazard was reduced, however, when the pressurised fuel system was replaced by one using wind-driven fuel pumps late in 1917,[29] although this was not initially adopted by American-built aircraft.[33] The otherwise inferiorDH.9 brought the pilot and observer closer together by placing the fuel tank in the usual place, between the pilot and the engine.
Despite its success, numbers in service with the RFC actually started to decline from spring 1918, mainly due to a shortage of engines, and production switched to the DH.9, which turned out to be disappointing, being inferior to the DH.4 in most respects. It was left to the further developedDH.9A, with the American Liberty engine, to satisfactorily replace the DH.4.
When theIndependent Air Force was set up in June 1918 to carry outstrategic bombing of targets inGermany, the DH.4s of 55 Squadron formed part of it, being used for daylight attacks.[22] 55 Squadron developed tactics of flying in wedge formations, bombing on the leader's command and with the massed defensive fire of the formation deterring attacks by enemy fighters.[34] Despite heavy losses, 55 Squadron continued in operation, the only one of the day bombing squadrons in the Independent Force which did not have to temporarily stand down owing to aircrew losses.[35]
After theArmistice, the RAF formedNo. 2 Communication Squadron, equipped with DH.4s to carry important passengers to and from theParis Peace Conference. Several of the DH.4s used for this purpose were modified with an enclosed cabin for two passengers at the request ofBonar Law.[36] One of these planes was extensively used by Prime MinisterDavid Lloyd George and was sometimes calledLloyd George's airplane - probably the first aeroplane widely used by a political leader.[37][38] Modified aircraft were designated DH.4A, with at least seven being converted for the RAF, and a further nine for civil use.[39]
At the time of its entry into the war, theUnited States Army Air Service lacked any aircraft suitable for front line combat. It therefore procured various aircraft from the British and French, one being the DH.4. As theDH-4, it was manufactured mostly by Dayton-Wright and Fisher Body for service with the United States from 1918, the first American built DH-4 being delivered to France in May 1918, with combat operations commencing in August 1918.[40][41] The powerplant was a 400 hp (300 kW)Liberty L-12 and it was fitted with two forward-firing .30 in (7.62 mm)synchronizedMarlin-Rockwell M1917 (a development of theColt-Browning) machine guns in the nose and two .30 in (7.62 mm)Lewis guns in the rear and could carry 322 lb (146 kg) of bombs. it could also be equipped with various radios like theSCR-68 for artillery spotting missions. The heavier engine reduced performance compared with the Rolls-Royce powered version, but as the "Liberty Plane" it became the US Army Air Service standard general purpose two-seater, and on the whole was fairly popular with its crews.
Aircrew operating the DH-4 were awarded four of the sixMedals of Honor awarded to American aviators.First LieutenantHarold Ernest Goettler andSecond LieutenantErwin R. Bleckley received posthumous awards after being killed on 12 October 1918 attempting to drop supplies to theLost Battalion of the77th Division, cut off by German troops during theMeuse-Argonne Offensive;[40] while Second LieutenantRalph Talbot andGunnery SergeantRobert G. Robinson of theUnited States Marine Corps (USMC) were awarded the Medal of Honor for beating off attacks from 12 German fighters during a bombing raid over Belgium on 8 October 1918.[42][43][better source needed] The type flew with 13 U.S. squadrons by the end of 1918.[44]
Following the end of the First World War, America had a large surplus of DH-4s, with the improved DH-4B becoming available, although none had been shipped to France. It was therefore decided that there was no point in returning aircraft across the Atlantic, so those remaining in France, together with other obsolete observation and trainer aircraft, were burned in what became known as the "Billion Dollar Bonfire".[45][41] With limited funds available to develop and purchase replacements, the remaining DH-4s formed a major part of American air strength for several years, used for many roles, with as many as 60 variants produced.[46] DH-4s were also widely used for experimental flying, being used as engine testbeds and fitted with new wings. They were used for the first trials ofair-to-air refueling on 27 June 1923, and one carried out an endurance flight of 37 hours, 15 minutes on 27–28 August, being refueled 16 times and setting 16 new world records for distance, speed and duration.[47] The DH-4 remained in service with theUnited States Army Air Corps, successor to the United States Army Air Service, until 1932.[48]
A large number of DH-4s were also used by theUnited States Navy and United States Marine Corps, both during the First World War and postwar. The Navy and Marine Corps received a total of 51 DH-4s during wartime, followed by 172 DH-4B and DH-4B-1 aircraft postwar and 30 DH-4M-1s with welded steel-tube fuselages (redesignated O2B) in 1925.[49] They remained in service with the Marine Corps until 1929, being used against rebel factions inNicaragua in 1927, carrying out the first dive-bombing attacks made by U.S. military forces.[49] The U.S. Navy converted some DH-4M-1s into primitive air ambulances that could carry one stretcher casualty in an enclosed area behind the pilot.[50]
Following the end of the First World War, large numbers of DH.4s and DH.4As were used to operate scheduled passenger services in Europe by such airlines asAircraft Transport and Travel,Handley Page Transport and the Belgium airlineSNETA.G-EAJC of Aircraft Transport and Travel flew the first British commercial passenger service fromHounslow Heath Aerodrome toParis Le Bourget on 25 August 1919, carrying a reporter from theEvening Standard newspaper and a load of newspapers and other freight.[51][52] They were used by Aircraft Transport and Travel until it shut down in 1920, while Handley Page Transport and SNETA continued operating the DH.4 until 1921. One aircraft was used byInstone Air Lines until its merger intoImperial Airways in 1924.[53]
On September 4, 1922,Jimmy Doolittle made the first cross-country flight, flying a de Havilland DH-4 – which was equipped with early navigational instruments – from Pablo Beach (nowJacksonville Beach), Florida, toRockwell Field, San Diego, California, in 21 hours and 19 minutes, making only one refueling stop atKelly Field.
The DH.4 were also used by theAustralian airlineQANTAS, flying its firstairmail service in 1922.[55] Twelve DH.4s forming part of theImperial Gift toCanada were used for forestry patrol and survey work, spotting hundreds of forest fires and helping to save millions of dollars worth of timber, with the last example finally being withdrawn in 1927.[56][10]
TheU.S. Post Office also adopted the DH-4 to carry air mail.[57][58] The Service acquired 100 of them from the army in 1918, and retrofitted them to make them safer, denominating them as the DH.4B.[57] In 1919, the DH-4B was standardised by the US Post Office, being modified to be flown from the rear cockpit with a 400 lb (180 kg) watertight mail compartment replacing the forward cockpit. The airmail DH-4B were later modified with revised landing gear and an enlargedrudder.[59] DH-4s were used to establish a coast-to-coast, transcontinental airmail service, between San Francisco and New York, a distance of 2,680 mi (4,310 km), involving night flight, the first services starting on 21 August 1924. The DH-4 continued in Post Office service until 1927, when the last airmail routes were passed to private contractors.[60]
War-surplus DH-4s were available cheaply in sufficient quantities to stimulate the development of "utility aviation": surveying, commercial photography, law enforcement, agricultural applications and other practical applications.[61]
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DH-4:
DH-4B:
DH-4M-1
DH-4M-2A
Data fromThe British Bomber since 1914,[8]The de Havilland DH.4[89]
General characteristics
Performance
Armament
Related development
Related lists
