The Ancestry Card Catalog entry for this addition is: UK, Royal Air Force Operations Record Books, 1911-1963, Military, 758,658 records. The original data source is AIR 27 Air Ministry and successors: Operations Record Books, Squadrons Record books 1911-1993 at the National Archives, Kew.
Although you can search by name the roster is far from complete. If you know the squadron and date you may find a complete crew list and description of the flight as I did for the accident that killed my uncle. Knowing that I was able to scroll back and find some earlier flights on which he served.
Contrary to Ancestry’s title, the collection is not just for the RAF. Australian, Canadian, Indian, Malayan, New Zealand, Rhodesian, South African, even Yugoslav OPBs are included.
Squadrons 400 to 443, and 162, 664 to 666 are Canadian, 450 to 467 are Australian, 485 to 490 New Zealand. There were crews of mixed nationalities.
As with battalion diaries, ORBs commonly mention officers by name, only counts of other ranks.
Findmypast and TheGenealogist have similar collections.