Michael Caine has been Chris Nolan's good luck charm ever since Batman Begins in 2005. He's appeared on-screen in every Nolan film since – The Prestige, The Dark Knight, Inception, The Dark Knight Rises and Interstellar – which is why his absence in this year's Dunkirk felt like a bit of an oddity. Well, the universe has been re-balanced. He did in fact have a minor cameo appearance!
Now, not to brag too much (okay, maybe a little), I spotted what I thought was Michael Caine's voice speaking to Tom Hardy's Farrier over the radio during the opening minutes, but then dismissed it because I assumed more people would've mentioned him. Turns out I wasn't alone in thinking that; here's what the director had to say when asked about it by NJ.com:
“Yes, good for you for spotting him. It's shocking to me that a lot of people haven't, when he has really one of the most distinctive voices in cinema. I wanted very much to squeeze him in here. It's a bit of a nod to his character in Battle of Britain. And also, it's Michael. He has to be in all my films, after all."
To quote J.K. Rowling's closing line in Harry Potter and the Deathly Hallows: "All was well."