British military service The DH.4 entered service with the RFC in January 1917, first being used by
No. 55 Squadron. 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. While
Russia 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. 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. In another incident, a group of four RNAS DH.4s were jointly credited with the sinking of the German
U-boat UB 12 on 19 August 1918. The DH.4 proved a huge success and was often considered the best single-engined bomber of World War I. 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, so that the DH.4 often did not require a fighter escort on missions, a concept furthered by
de Havilland in the later
Mosquito 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. There was also some controversy (especially in American service) that this placement of the fuel tank was inherently unsafe. In fact, most contemporary aircraft were prone to catching fire in the air. The fire hazard was reduced, however, when the pressurised fuel system was replaced by one using wind-driven fuel pumps late in 1917, The otherwise inferior
DH.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 developed
DH.9A, with the American Liberty engine, to satisfactorily replace the DH.4. When the
Independent Air Force was set up in June 1918 to carry out
strategic bombing of targets in
Germany, the DH.4s of 55 Squadron formed part of it, being used for daylight attacks. 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. After the
Armistice, the RAF formed
No. 2 Communication Squadron, equipped with DH.4s to carry important passengers to and from the
Paris Peace Conference. Several of the DH.4s used for this purpose were modified with an enclosed cabin for two passengers at the request of
Bonar Law. One of these planes was extensively used by Prime Minister
David Lloyd George and was sometimes called ''Lloyd George's airplane'' - probably the first aeroplane widely used by a political leader. Modified aircraft were designated DH.4A, with at least seven being converted for the RAF, and a further nine for civil use.
United States military service At the time of its entry into the war, the
United 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 the
DH-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. The powerplant was a
Liberty L-12 and it was fitted with two forward-firing
synchronized Marlin-Rockwell M1917 (a development of the
Colt-Browning) machine guns in the nose and two
Lewis guns in the rear and could carry of bombs. it could also be equipped with various radios like the
SCR-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 six
Medals of Honor awarded to American aviators.
First Lieutenant Harold Ernest Goettler and
Second Lieutenant Erwin R. Bleckley received posthumous awards after being killed on 12 October 1918 attempting to drop supplies to the
Lost Battalion of the
77th Division, cut off by German troops during the
Meuse-Argonne Offensive; The type flew with 13 U.S. squadrons by the end of 1918. 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". 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 of
air-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. The DH-4 remained in service with the
United States Army Air Corps, successor to the United States Army Air Service, until 1932. A large number of DH-4s were also used by the
United 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. They remained in service with the Marine Corps until 1929, being used against rebel factions in
Nicaragua in 1927, carrying out the first dive-bombing attacks made by U.S. military forces.
Civil use 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 as
Aircraft Transport and Travel,
Handley Page Transport and the Belgium airline
SNETA.
G-EAJC of Aircraft Transport and Travel flew the first British commercial passenger service from
Hounslow Heath Aerodrome to
Paris Le Bourget on 25 August 1919, carrying a reporter from the
Evening Standard newspaper and a load of newspapers and other freight. 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 by
Instone Air Lines until its merger into
Imperial Airways in 1924. 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 (now
Jacksonville Beach), Florida, to
Rockwell Field, San Diego, California, in 21 hours and 19 minutes, making only one refueling stop at
Kelly Field. The DH.4 were also used by the
Australian airline
QANTAS, flying its first
airmail service in 1922. Twelve DH.4s forming part of the
Imperial Gift to
Canada 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. The Service acquired 100 of them from the army in 1918, and retrofitted them to make them safer, denominating them as the DH.4B. DH-4s were used to establish a coast-to-coast, transcontinental airmail service, between San Francisco and New York, a distance of , 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. 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. ==Variants==