One of the most important aircraft in the early RAF. The Avro 504 began development in late 1912 (at A.V. Roe), first flew in July 1913, and was in service at the start of the First World War, serving with both the RFC and the RNAS. The RFC used the 504 for reconnaissance and gun spotting, and rarely had more than one or two of the type with any squadron, and none after mid-1915. The RNAS used the 504 as a strategic bomber early in the war, starting with a raid on the Zeppelin sheds at Friedrichshafen on Lake Constance (21 November 1914), where a lucky strike on the gas plant caused most damage, but later raids did little damage.
The true value of the 504 was as a pilot trainer. It's design made it safe to fly, but hard to fly with skill, the ideal balance for a trainer, and from 1916 both the RFC and RNAS used it as their standard training craft. The 504 was adopted in the same role by the RAF, and after the end of the war it's use spread to most commonwealth airforces, as well as Russia and Japan. The last model, the 504N was produced from 1927 until 1933, and during the twenty years of it's manufacture nearly 9,000 were produced, some of which were still in use at the start of the second world war.