Based at Ricall Airfield during the Second World War. It was a Heavy Conversion Unit for Halifax bombers.
With the introduction of the new heavy bombers, the 4-engined Short Stirling, Avro Lancaster and Handley Page Halifax, into service, the Royal Air Force introduced Heavy Conversion Units. The Heavy Conversion Units began forming in late 1941 to qualify crews trained on medium bombers to operate the heavy bombers prior to assignment to an Operational Training Unit to gain experience before final posting to the operational squadrons.
After the end of the war their role was taken over by the Operational Conversion Units. Although the units had nominal bases it was usual for different flights and individual aircraft to be detached nearer the operational bases. Some of the Heavy Conversion Units were involved in bombing operations over Germany.
A satellite airfield controlled by Marston Moor near York and was home to 1658 Heavy Conversion Unit. The airfield was laid out on what was Riccall and Barlby Commons. It consisted of three concrete and asphalt runways, six T2 and one B1 hangers.
The Halifax conversion unit of 76 and 78 moved into Riccall in the September of 1942 in October they formally merged to form 1658 Heavy Conversion Unit (HCU) and in the November they were joined by 158 Conversion Unit which reformed a C Flight 1658, this addition brought the unit up to full strength - 32 Halifax aircraft.
Riccall was home to 1332 TCU flying Avro Yorks and Short Stirlings converted to a freight role,
Moved to Dishforth and all flying at Riccall ended. The base was used for storage before being sold off for farmland later.