I've just looked up the qualifications for the Defence Medal in British Battles and Medals by Major Gordon, still regarded as "the bible" for campaign medals. Gordon lists 14 different ways to qualify for the medal, including those already mentioned by Easy Street - no wonder some people got confused by it. I suspect that qualification requirements for this new Op Shader medal will be amended in due course.
gijoe your father would certainly have been entitled to the War Medal 1939-45 as well as the Defence Medal, but if you meant that there was no campaign star awarded for those operations then you are of course correct.