Does anyone know what proof you have to give that your father was French? He passed away years ago. He served in the French Navy. Would proof of that be good enough?
France has double ius soli, which means that a child born in France to at least one French-born parent is legally a French citizen. Therefore, if you can prove that your father and one of his parents were born in France, you would have French citizenship. If you can get hold of any official document that states the place of birth, that would help your cause – preferrably one issued by a French authority. If you don't have documents but know their place of birth, you might be able to get a copy of the birth certificates.