"Kairei" returned in May 1998, cruise KR98-05, with ROV "Kaikō", under the direction of chief scientist Jun Hashimoto with both geophysical and biological goals. Their bathymetric survey from 14–26 May was the most intensive and thorough depth and seismic survey of the Challenger Deep performed to date. Each evening, "Kaikō" deployed for about four hours of bottom time for biological-related sampling, plus about seven hours of vertical transit time. When "Kaikō" was onboard for servicing, "Kairei" conducted bathymetric surveys and observations. "Kairei" gridded a survey area about 130 km N–S by 110 km E-W. "Kaikō" made six dives (#71 - #75) all to the same location, (11°20.8' N, 142°12.35' E), near the bottom contour line in the western basin.