Despite harsh weather and ocean conditions, and complex geological characteristics of its drill site, the deep-sea drilling vessel Chikyu, for the first time in the history of scientific ocean drilling, conducted riser-drilling operations to drill successfully down to a depth of 1,603.7 meters beneath the seafloor (at water depth of 2,054 meters). Engaged in the Integrated Ocean Drilling Program (IODP) Expedition 319, the Chikyu is drilling deep into the upper portion of the great Nankai Trough earthquake zone to gain insights into geological formations and stress-strain characteristics.