JS - Your father's DFC is mentioned as being awarded on 21 Jan 1944 -
Supplement to London Gazette 21 Jan 44
You'll see that there are some citations given, but not for your father. It may be that this points to the award being at the end of a tour, and recognising consistent gallantry on his part throughout it, rather than for one specific event. I'll have a look at the record of DFCs awarded when I'm in work and see if there's a citation - unless someone with the book has it and can beat me to it.