List of conversion units of the Royal Air Force
Conversion units and operational conversion units (OCUs) were training units of the Royal Air Force (RAF). == History == With the introduction of new heavy bombers, the four-engined Short Stirling, Avro Lancaster, and Handley Page Halifax, the Royal Air Force introduced heavy conversion units (HCU).
Source: Wikipedia — List of conversion units of the Royal Air Force (CC BY-SA 4.0)