My credibility is that he is a former admiral which means he doesn't get access to know what the U.S. plans are, organization or the technology know how. Do you think he know the location of all the subs? No. Do you think he as a former admiral can tell the Pentagon what to do? No. In other words his has no influence, and from where I'm sitting, the U.S. military is ignoring his pleas in dealing with China.
He does not have to know the location of the subs or how many ships are being build or influence the Pentagon. He draws the conclusion in the event of war the West has no chance to win and will face the onslaught inflicted by China. You have trouble accepting this little fact?