Ko-ichi Nakamura had been engaged in marine geological research for a quarter century at the Geological Survey of Japan, which merged with the National Institute of Advanced Industrial Science and Technology (AIST) in 2001. He started studying redox of hydrothermal fluid by electrodes after he found the first backarc hydrothermalism in the Okinawa Trough with Peter Halbach. He has been sailing with VENTS program personnel since 1993 and with Marvin Lilley and other UW people since 1998 mainly in the Pacific hydrothermal sites. He was on-board explorer at 2002, 2003 and 2004 Submarine Ring of Fire expeditions. He supplied redox sensors for ABE and CTD operation at the Lost City 2003 expedition. In this cruise the redox sensor on the Hercules' second manipulator is expected to point out the existence of invisible fluid emission.