He told me one evening as he drove his elderly Daimler between Brize Norton and Burford during the war. He had been one of the three regular R.A.F. officers who had been chosen to give a display of aerobatics before delighted and awe-struck crowds at the Hendon Air Pageant. Nesbitt-Dufort - he didn't become "Whippy" until some hours later - threw his aircraft gaily about the sky, looping the loop linked on to two other aircraft in perfect precision. When the display was over, he set course for base. High over Bedfordshire, an engine began to splutter. Nesbitt-Dufort looked anxiously for somewhere to land. He found it. From the air it looked almost too easy, a flat, greeny expanse of field or meadow with no trees or other obstructions. He came down, and at about a hundred feet, his engine packed up. Using every eddy of the air, he did a perfect forced landing on the perfect field, skimming along the grass, braking to a stop as he ran up a gentle incline. He drew a deep breath, and wiped the sweat off his forehead. Then he looked around - and was electrified to see that he was not alone. A gigantic rhinoceros was trotting ponderously in his direction, head lowered. At the same instant, he heard the deep-throated roaring of lions and, as he bolted for the stout fencing, he acquired his nickname. Flight-Lieutenant Nesbitt-Dufort had put down in the middle of Whipsnade Zoo.
Reference: Jerrard Tickell (1956), Moon Squadron, Allan Wingate (p 37 of the 1960 Hodder and Stoughton paperback edition)