Japan’s Kaikō ROV was the first vehicle to sample mud from the bottom of Challenger Deep.
Built and operated by the Japan Agency for Marine-Earth Science and Technology, Kaikō made its first Challenger Deep descent in March 1995. It returned during later expeditions and collected sediment and biological material from the trench floor. The vehicle obtained more than 360 sediment samples, allowing researchers to study organisms living under pressures exceeding 1,000 times atmospheric pressure at sea level.
Kaikō was a remotely operated vehicle, not a crewed submarine. Its support ship was RV Yokosuka, and operators controlled the vehicle through a tether from the surface. The ROV reached a measured depth of about 10,911.4 m during its early Challenger Deep work, then continued scientific dives elsewhere.
The names in the alternatives are easy to confuse because Japan has operated several deep-sea vehicles. Shinkai was a different submersible, while Urashima was an autonomous underwater vehicle. ABISMO was developed later as a replacement for Kaikō, which was lost at sea in 2003 during Typhoon Chan-Hom.