Well that all depends upon which Air Force you might be refering to. In the US all Air Force and Navy pilots will have a degree as it is a requirement in order to be an officer. Canada used to not be a requirement but has now said that it is a must. Australia, NZ and the UK I believe is not a must. My experience has been about half will have a degree and out of those half only 1/4 will actually have one which could be applied to aviation.