227 OCU was the OCU for the airborne observation post squadrons. 235 was the flying boat conversion unit. Both were then redesignated (or disbanded and reformed under a new name, dependent upon source material); 227 became the AOP School and 235 the Flying Boat Training squadron (the nomenclature used for the unit at formation in 1939).The former unit disbanded when the AAC was formed; the latter in 1956 to reflect the reduction in the need for crews as the Sunderland headed towards final retirement.