Given what I know about Christopher Nolan as a filmmaker, I would expect a heavier emphasis on practical effects. However, even with movies like Fury Road, where practical effects were used heavily, CGI still played an important role in the final film.
I know that Dunkirk was shot on 70mm film; which makes it fundamentally different from most modern films. Even so, I would expect that essentially every big-budget film today used at least some CGI. However, my wife pointed out that CGI may not be possible given that it was filmed with actual film and not digital.
So a 2-part question: was any CGI used? And if so, how is it possible to use CGI on actual film?