https://www.theguardian.com/books/20...arthurcclarke1
At 17 he joined the British Interplanetary Society, an organisation then widely regarded as crackpot, but of which he was later to be treasurer and, eventually, chairman.
In the civil service his mathematical ability took him into the audit branch. But, after the outbreak of the second world war, he opted to join the RAF where, via electronics training, he became an instructor at radio school. Finally he went to work on the development and proving of American ground control approach - talk-down - radar at Davidstow Moor in north Cornwall, a system which pilots never liked because it robbed them of control until the last moments.