How many movies have Peter Sellers and Robert O'Neil acted in together?

They have worked on 2 movies together! Their first movie together was The Mouse That Roared (1959) while their highest rated movie together was Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb (1964). They have not worked together since Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb (1964).