Caldwell was part of the famed No. 60 Squadron of the British Royal Flying Corps (which later became the Royal Air Force). He became such an expert pilot that he was promoted and given his own squadron, No. 74 Tiger Squadron. Even though he was a commander, he still insisted that he fly to the front lines, because he knew it was his destiny to soar through the air and brazenly dare Death to take him.
During one mission, Caldwell managed to crash his plane into another in mid-air (it was destined to happen, really). This damaged his aircraft's wing bad enough that it went into a death spiral, meaning Caldwell was doomed to a dizzy plummet into the ground followed by a very fiery death. But Caldwell, being insane, took a moment to determine that he just needed to change the center of gravity -- that is, add some weight to the side with the damaged wing, to balance things out. So, while the plane was still spinning, he somehow climbed out onto the m***********g wing, reaching into the cockpit and piloting the aircraft from there. It looked something like this:
via Cambridge Air Force
"Who am I kidding, I damaged the plane just so I could try this."
It worked, too. Sort of. It stabilized the aircraft long enough that he was able to guide the plane back over friendly territory. Landing the thing from the wing was out of the question (come on, that would be beyond crazy), so Caldwell tried to find a good spot in the battle-scarred landscape to try to not die a spectacular death.