The survey work takes another couple of weeks. They figure out where the shore of Lake Yamamoto will be and calculate its volume. It will be more of a pond than a lake—less than a hundred meters across—but it will be deceptively deep, and it will hold a lot of water. They calculate the angle of the shaft that will connect the bottom of the lake to the main network of tunnels. They figure out where all of the horizontal tunnels will emerge from the walls of the Tojo River’s gorge, and stake out the routes of roads and railways that will lead to those openings, so that debris can be removed and precious war material brought in for storage. They double- and triple-check all of it to make sure that no fragment of the works will be visible from the air.