Non-specialist readers will know, and perhaps remember, the participation in World War II of such aircraft as the Avro Anson and Lancaster. They may not have heard of the Avro 504, yet this little two-seat trainer must be numbered among the great aircraft of British aviation history.

The 504 was designed in 1912 and it was decided to introduce this aircraft to the aviation scene by entering it for the second Aerial Derby, which was scheduled for 20 September 1913, to gain as much interest and free publicity as possible. Thus, it was built behind closed doors and when subsequently flown to Hendon to take part in the race it was seen in public for the first time. It was perhaps something of an anticlimax that it did not win, coming in fourth at an average 107km/h. But this was a considerable achievement for an aircraft first flown only three days previously.

Production of 12 504s for the War Office began in the summer of 1913, the first of more than 8,000 for military service to be built during World War I. Successive variants were to remain in production for almost 20 years. The last to be operated by the RAF were seven civil 504N impressed for service in 1940 and used for glider-towing.

The 504 was designed for training and private flying, and few could have foreseen that this aircraft would ever be flown in anger. Yet when the RFC's No 5 Squadron flew to France on 13 August 1914, its small force included several 504s.

Although little used in military operations, the type is remembered for an attack on the German Zeppelin sheds at Friedriehshaven, carried out on 21 November 1914 by three 504s of the RNAS, each armed with four 9kg bombs. One Zeppelin was destroyed in its shed and hits on the associated gasworks resulted in an explosion which caused great damage.

This lightweight but robust biplane proved to be a superb training aircraft. When Maj R. R. Smith-Barry became commander of No 1 Reserve Squadron at Gosport in 1916, he evolved a completely new system of flying instruction based on demonstration and explanation. So good were the results that this squadron was developed into the School of Special Flying - using the Smith-Barry system and Avro 504J - with pupils encouraged to fly these aircraft to the limit of their capabilities. Later 504Ns were equipped especially for use by the RAF's Central Flying School, becoming the first instrument or blind-flying trainer to serve with the RAF.

Extensively built by A. V. Roe for home and export customers, in both civil and military guises, 504s were also built by manufacturers in Australia, Belgium, Canada, Japan, Netherlands East Indies, and Russia.

In an era when the general public regarded aviation as a form of transportation suited only to the brave or foolhardy, the 504 was used by Sir Alan Gobham's "Flying Circus" and Capt Percival Phillips' Cornwall Aviation Company, carrying large numbers of civilians on their first flight. It has been reported that Capt Phillips alone carried something like 91,000 passengers into the air, the majority of them in an Avro 504.