| DH4 | The DH.4 entered service with the RFC in January 1917, first being used by No. 55 Squadron. 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. As well as the RFC, the RNAS also used the DH.4, both over France and over Italy and the Aegean front. The DH.4 was also used for coastal patrols by the RNAS. One, crewed by the pilot Major Egbert Cadbury and Captain Robert Leckie (later Air Vice-Marshal) as gunner, shot down Zeppelin L70 on 5 August 1918. Four RNAS DH.4s were credited with sinking 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 in World War II.
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,[11] although this was not initially adopted by American-built aircraft.[14] 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. 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.[15] 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 Andrew Bonar Law. These aircraft were designated DH.4A, with at least seven being converted for the RAF, and a further nine for civil use |
