Many scientists have participated at these Kaiko cruises. Three legs have been studied. The observations show that the trenches around Japan exhibit a whole range of possible subduction processes. It has been demonstrated that the subduction could fairly "swallow" as sharp-pointed fishbones as volcanoes as Fuji Yama or as big lumps as the palau Kyushu volcanic arc. The subduction then changes into collision and these surveys provide the first indications about the way. The transition from the Nankai trench to the Izu collision takes place. Such transition is accompanied by an oceanic lithosphere overthrust. Last, it appears that scars exhibited by the oceanic lithosphere in the form of fossil rift valleys and faults are reactivated upon the bending of the plate in the trench and play a key role in the determination of the network of seismically active faults.