Spuk,
Its a few years out of date but i dont think its changed much
Armed Forces - r4a2 - RAF Air Command - Operational Conversion Unit (OCU)
Also (Please correct if needed) many Squadrons like 27SQN (Chinooks) have OCF's Operational Conversion Flight's. In which case, they wont be listed with the other SQN's like 203(R) OCU Sea King.
Hope that helps,
FUBAR