With his father, Robert Bourdillon, he developed the closed-circuit oxygen apparatus used by Charles Evans and himself on their pioneering climb to the South Summit of Everest on 26 May 1953. Bourdillon could well have been either the first or second man to officially summit Everest but was forced back when Evans' oxygen system failed. The pair came within three hundred feet of the Main Summit; both turning back after reaching the South Summit. Three days later, Hunt directed Edmund Hillary and Tenzing Norgay to go for the Main Summit (using open-circuit equipment); which they reached on 29 May 1953. Bourdillon never attempted an Everest expedition again.