Yeah, that's Boeing Plant #2 hidden under that fake suburban subdivision. They tried to make it match the neighborhood on the other side of the Duwamish River. The plant is currently being torn down having fallen into disuse and decay.
In retrospect it seems like a great deal of effort, considering no land based Japanese plane had the range to strike Seattle and the IJN carriers were too busy elsewhere, but the panic after Pearl harbor on the West Coast at the time was real enough. San Francisco had three air-raid alerts on the first night of the war.