It was not until the 1930s that the Army realised it might once again need its own pilots. In 1933, an article appeared in the journal of the Royal United Services Institute written by Captain HJ Parham of the Royal Artillery (RA). It criticised the existing method of directing artillery fire from the Army co-operation aircraft by use of Morse code over a one way wireless and responses by means of ground signals. The Army Cooperation pilots would be briefed for the sortie at a distant airfield; there was considerable delay before the target could be engaged. Captain Parham suggested that a light aircraft flown by a gunner officer and with two way radio would be much more effective
As the dark clouds of war gathered in 1939, key officers realised the need for the Army to get back into the air, notably Major Charles Bazeley RA, who lobbied the Ministry of Defence for a simple, rugged reconnaissance aircraft. The Royal Artillery Flying Club at Larkhill conducted a number of trials to develop this idea and as the Club's secretary, Major Bazeley persuaded the War Office, with Air Ministry agreement, to hold official trials in 1939 but using the current Army Cooperation in service aircraft, the Westland Lysander.
The trials for the Westland Lysander were successful but, although a fine aircraft, it was no match for enemy aircraft and was often shot down. This was particularly evident in May 1940 where the events of Dunkirk overshadowed attempts to develop the Air Observation Post (AOP) Squadron. Major Bazeley persisted and 651 AOP Squadron Royal Air Force was formed at Royal Air Force Old Sarum in August 1941, equipped with the British Taylorcraft Auster AOP Mk I, known subsequently as the 'Auster'. The Squadron saw action in Tunisia in November 1942 and was given the improved performance Auster III. These aircraft operated from field airstrips close to the artillery units they supported and learnt to evade enemy fighters by developing 'nap of the earth' flying techniques. Before the end of the war, a further 15 Squadrons were formed, including one Polish and three Canadian. They fought in all major operational theatres during the Second World War (1939-1945)
In 1944-1945 the Squadrons were equipped with the Auster IV and V with the American Lycoming engine. The Lysander and Auster became the eyes and ears of the Army. The Auster also became famous amongst the rank and file for delivering much needed ammunition and supplies as well as evacuating casualties. After the war most AOP Squadrons were disbanded but those that survived were soon pressed into service in Palestine, Malaya, Korea and Cyprus using the Auster VI. This continued as the main AOP aircraft with the Auster VII as the training equivalent. The Auster IX was brought into service in 1946 and continued for 11 years until the AOP Sqns were subsumed into the newly formed Army Air Corps on 1st September 1957.