What was the largest concentration of battleships in the Second World War?
Short answerPearl Harbor, because the battleships were present together at one time rather than rotating through a larger campaign deployment.
NotesPearl Harbor held the largest concentration of battleships in the Second World War. Concentration is different from total deployment. Okinawa involved many battleships, but they rotated and were not all simultaneously in the same place. Pearl Harbor's significance in this comparison is the density of capital ships present at once.