Map from World War II

My daddy brought this map back from the Philippines after W.W.II. Written on the back is that it was "Jap Owned." There are Japanese characters all over the back and notes on the map itself concerning ships that were attacked, spots where fellow soldiers were killed, etc. Daddy was a medic, so he probably noted the exact spot on this map. I have it folded, wrapped in plastic wrap and in a trunk. I have no idea what the characters mean.