During the Second World War he was trained as an officer at Sandhurst and Aldershot[2] and became a commando, being one of the first to parachute into Arnhem during the relief of the Netherlands by Allied troops.
In the 1960s, the Hungarian-born American film and TV producer Ivan Tors came to Kenya on holiday and visited an animal orphanage set up by Dr Harthoorn and his wife, Sue Hart.
Tors was so impressed by the idea that he developed a TV series named Daktari (Swahili for 'doctor') which ran in syndication worldwide for several decades.
With Kenyan independence (1963) Dr Harthoorn's position as senior lecturer at the veterinary college in Nairobi was abruptly terminated (he was replaced without notice by one of his PhD students).
He also had a vital role in the saving of thousands of animals marooned on small islands created by the rising waters of the newly formed Kariba Dam in 1959-1960 in Southern Rhodesia (Zimbabwe).