As a result of the Smuts reports of Jun and Oct 1917 which reviewed the future of air fighting arrangments, the Air Force (Constitution) Act of Nov 1917 created the Royal Air Force by amalgamating the Royal Flying Corps and Royal Naval Air Service on 1 Apr 1918. It was an unpopular decision, but driven through against almost overwhelming opposition, largely by Sir Hugh Trenchard and a small group of ex-Army officers. A period of contraction occurred after World War I, followed by an expansion programme from 1934. Then in May 1939, the units of the Fleet Air Arm of the Royal Air Force were returned to Royal Navy control.
The RAF was active in many types of flying but the first steps with rotary wing machines, in the form of a few Cierva autogyros began to be introduced late in the 1930s, largely as a means of calibrating the radar equipment used in the various Chain Home family of systems. These were followed by the first true helicopter in the Hoverfly R-4 in 1945 and the introduction to service of the Sycamore and Dragonfly by the end of 1953. On 1 Sep 1957, the RAF relinquished its Air Observation Post (AOP) Squadrons and Light Liaison Flights to the newly formed Army Air Corps.
Since 1 Oct 1999, when Joint Helicopter Command was formed, the RAF has committed 7, 18, 27, 33 & 230 Squadrons with their Chinook, Puma and (from 2002), 28(AC) Squadron with its Merlin helicopters to this tri-service organisation.
With effect from Nov 2007 78 Sqn was re formed at RAF Benson to fly the Merlin HC3A. The RAF brought these six Merlins from the Danish Air Force to boster the Support Helicopter Force.
Following an outcome of the 2010 Defence SDSR, 78 Sq (Joint Helicopter Command) passed its Merlins in Sep 2014 to 846 NAS as part of the fleet transfer to the Commando Helicopter Force.