No. 661 Squadron AAC is a squadron of the British Army's Army Air Corps (AAC). It was formerly No. 661 Squadron, a Royal Air Force air observation post squadron associated with the Canadian 1st Army and later part of the Royal Auxiliary Air Force. Numbers 651 to 663 Squadrons of the RAF were air observation post units working closely with British Army units in artillery spotting and liaison. A further three of these squadrons, 664–666, were manned with Canadian personnel. Their duties and squadron numbers were transferred to the Army with the formation of the Army Air Corps on 1 September 1957.

The Army Air Corps (AAC) is the aviation arm of the British Army, first formed in 1942 during the Second World War by grouping the various airborne units of the British Army. Today, there are eight regiments of the AAC, as well as two independent flights and two independent squadrons deployed in support of British Army operations around the world. Regiments and flights are located in the United Kingdom, Kenya, and Canada. Some AAC squadrons provide the air assault elements of 16 Air Assault Brigade, through Joint Helicopter Command.