On February 9, a commercial satellite passing over the Bohai Shipyard at Huludao photographed a submarine in a flooded drydock, and for a few days, the analysts who watch that yard assumed it was routine. Initial low-resolution imagery suggested just another Type 093B, the guided-missile boat China has been turning out at a steady clip. Then, sharper pictures and synthetic-aperture radar data arrived, and the assessment changed completely. The h…