Looking for US Navy bio father, based Spain 1970

Hi I am trying to find my biological father, but my mother can give me very little information: - first name was Arnie or Arne - she can't remember his surname, but it was Scandinavian - he is an American of Norwegian descent - he was based at US Navy base Rota, Spain in 1970 when they met - prior to being based in Spain, he may have been to Japan and Vietnam with the US Navy I have ordered the book I have seen recommended here on tracing people in the military, but wondered if anyone had any other advice on how to find him, given that I don't have a surname, date of birth or even know where he was from in the States (I am in the UK). Many thanks.