An air observation post (AOP) is an aeroplane or helicopter used in the role of artillery spotter by the British Army and Commonwealth forces.
[1][2] In the interwar period, the role of artillery spotting was mixed with reconnaissance and ground attack to be served by Army co-operation (AC) squadrons.
This training and development work had to be abandoned when the German blitzkrieg got underway and the unit was back at its UK base in Old Sarum, Wiltshire, by 20 May 1940.
Since most operations were carried out separately by individual flights, this lack of rank structure in squadrons tended not to produce problems.
The low speed, high manoeuvrability, small size (so aiding concealment at front-line landing grounds) and light weight of the Auster made this a much more suitable aircraft than the Lysander.
[4]: 155 An AOP flight operated during the Malayan Emergency, but was redeployed to Korea during the Korean War at the request of the 1st Commonwealth Division.