1664 HCU- Heavy Conversion Unit (RCAF) -

From the unit's own diary (Operations Record Book): the unit was at RCAF Station Croft until 6 December 1943; the main movement to Dishforth took place on 7 December 1943 and the unit became part of RCAF Station Dishforth. The diary file ends in December 1943.

The Croft station diary has the unit at Croft from June to December 1943; in 1944 it names the unit only as receiving personnel and aircraft from the Croft squadrons (aircraft transferred from 434 Squadron), never as resident.

The Dishforth station diary records the arrival of No. 1664 Conversion Unit from Croft in December 1943.

The unit's diary at Dishforth records two losses on training flights in 1944: on 14 October 1944 Halifax II HR802 failed to return from a cross-country 'bullseye' exercise (six aircraft searched the sea on the 15th without result and it was posted missing), and on 15 November 1944 a Halifax lost on a night cross-country at 18,000 feet collided with an aircraft of the Wombleton unit (F/L Garvie and crew).