In 1999, "Kairei" revisited the Challenger Deep during cruise KR99-06. The results of the 1998-1999 surveys include the first recognition that the Challenger Deep consists of three "right-stepping en echelon individual basins bounded by the depth contour line. The size of of the deeps are almost identical, 14-20 km long, 4 km wide." They concluded with the proposal "that these three individual elongated deeps constitute the 'Challenger Deep', and identify them as the East, Central and West Deep. The deepest depth we obtained during the swath mapping is in the West Deep (11°20.34' N, 142°13.20 E)." The depth was "obtained during swath mapping... confirmed in both N–S and E-W swaths." Speed of sound corrections were from XBT to , and CTD below .