It was a formal board. So knock, request to enter, salute the President of the Board, sit at attention the entire interview and maintain military bearing. I wore OCPs but I made sure I knew right time, right uniform and right place prior to the interview and asked if it was formal or informal. I was asked a series of questions and No interviews are ever the same. You just have to be quick with the responses, be confident and if you do not know the answer then ask to come back to it. Know the chain of command, know the regs having to do with that job description and be prepared for an odd question that has nothing to do with the job but instead helps them decide how quick you are to problem solve. I was called back the next day with the offer and accepted the position.