Oahu is, in political and military terms, the chief of the Hawaiian Islands. It measures about 30 miles from north to south and 40 miles from east to west, and is shaped like a rectangle tilted to the west with the southern corner bitten off. In the bay facing south a narrow entrance gives access to Pearl Harbor, a superb natural anchorage and the base of the American Pacific Fleet. Immediately east of the harbor is the capital city of Hawaii, Honolulu. Two ranges of mountains run along the east and west of the island with a saddle of flat land in the center where Wheeler Field and Schofield Barracks are located. The topography naturally divided the air strikes from the north into streams around the east and west coasts or down the middle of the island.
You can find out more about Oahu in the following Osprey book: