 His most famous image shows the children of hop pickers watching the aerial 'dogfights' of the Battle of Britain.It was used in a propaganda campaign alongside the slogan "Help England And It Won't Happen Here" which helped to convince millions of Americans to join the war against Nazi Germany.In 2009 the image was used to publicise 'Outbreak' - the major Imperial War Museum exhibition commemorating 70 years since the start of World War II.