1659 HCU- Heavy Conversion Unit (RCAF) -

From the unit's own diary (Operations Record Book): the unit was at RCAF Station Leeming from its formation in October 1942 until 13 March 1943; on 14 March 1943 all 22 aircraft were flown to Topcliffe, and the diary is headed Topcliffe from then to the end of the file in 1945.

The Leeming station diary records that 1659 Conversion Unit left RCAF Station Leeming and went to RCAF Station Topcliffe (March 1943). The unit is named in that diary only in the first months of 1943.

The Topcliffe diary, kept 'including 1659 Conversion Unit', records the unit's losses at Topcliffe: on 18 January 1944 at 10.30 Halifax LW334 crashed at Snilesworth Lodge near Kepwick, Yorkshire, and its six-man crew were all killed (a second Halifax of the unit crashed half a mile south-east of the airfield that morning); a night crash near Sutton Bank brought a requiem mass in the station chapel for those killed on 15 January (1945).

The unit's Form 541 for March 1945 lists crews on 'Sweepstake' duty with a target (for example a diversionary raid on 20 March 1945, target 48 40 N 07 00 E, in Halifax III LW689 and HX268), so heavy conversion unit crews were sometimes under battle orders.