Kaikō ROV

Lore & Background

Kaikō reached a maximum depth of 10,911.4 meters at the Challenger Deep on 24 March 1995, during its initial sea trials, collecting video and photographs of barophilic benthos including tubeworms and shrimp. In February 1996, it returned to Challenger Deep, collecting sediment and microorganisms at 10,898 meters, including the obligately barophilic bacteria Moritella yayanosii and Shewanella benthica. In December 1997, Kaikō located the wreck of Tsushima Maru off Okinawa, and in May 1998 it collected specimens of the amphipod Hirondellea gigas from the Challenger Deep. In October 1999, it performed a robotic mechanical operation at 2,150 meters off Okinawa near the Ryukyu Trench, discovering the violet-pigmented bacterium Shewanella violacea. In late November 1999, it located the wreckage of the H-2 No. 8 rocket at 2,900 meters off the Ogasawara Islands. In August 2000, Kaikō discovered hydrothermal vents and their associated deep sea communities at 2,450 meters near the Central Indian Ridge. On 29 May 2003, Kaikō was lost at sea during Typhoon Chan-Hom when a secondary cable connecting it to its launcher at the ocean surface broke off the coast of Shikoku Island.

Reader's Guide

Kaikō's significance lies in its pioneering role as the first unmanned submersible to reach the bottom of the Challenger Deep, and only the second vessel overall to do so since the Trieste mission in 1960. Its 250 dives between 1995 and 2003 yielded a substantial collection of 350 biological species, including 180 different bacteria, some of which may have medical and industrial applications. The discovery of obligately barophilic bacteria such as Moritella yayanosii and Shewanella benthica, which contain high levels of omega-3 fatty acids, opened avenues for potential treatments for hypertension and cancer. The bacterium Shewanella violacea, with its violet pigment, suggested possible uses in cosmetics and semiconductor manufacturing. Kaikō also contributed to deep-sea archaeology by locating the wrecks of Tsushima Maru and the H-2 No. 8 rocket, and to geology by discovering hydrothermal vent communities on the Central Indian Ridge. Its loss in 2003 led to the temporary use of Kaikō7000II, rated to 7,000 meters, and ultimately to the development of the 11,000-meter class ROV ABISMO, which began sea trials in 2007.

Did You Know?

• Kaikō was the second of only five vessels ever to reach the bottom of the Challenger Deep, as of 2019.
• It collected 350 biological species, including 180 different bacteria, during more than 250 dives.
• The bacterium Shewanella violacea, discovered by Kaikō, produces a brilliant violet pigment with potential applications in cosmetics and semiconductors.
• Kaikō was lost at sea on 29 May 2003 when a secondary cable broke during Typhoon Chan-Hom.

The Historic Challenger Deep Dive

In March 1995, Kaikō made history by becoming the second craft of any kind to touch the floor of the Challenger Deep, the deepest surveyed point in the world's oceans. This remarkable feat came thirty-five years after Don Walsh and Jacques Piccard had first descended in the Trieste bathyscaphe in 1960, and it marked the very first return to that extreme depth since their pioneering mission. During the dive, Kaikō recorded a maximum depth of 10,911.4 meters, a figure that stood as the deepest ever achieved by an unmanned submersible. The pressure at that level exceeds one thousand times standard atmospheric pressure, making the descent an extraordinary engineering and scientific accomplishment. Kaikō was not alone in this lineage; as of 2019, only five vessels in total had ever reached the Challenger Deep floor. The British HMS Challenger expedition of the 1870s had first identified the depression through crude sounding lines, and it was not until the late twentieth century that technology allowed repeated, detailed exploration of such an extreme environment. Kaikō's dive opened a new chapter in deep-ocean research, proving that unmanned platforms could rival and extend the reach of manned expeditions.

A Biological Treasure Trove

Between 1995 and 2003, Kaikō completed more than 250 dives that yielded an extraordinary haul of 350 biological species, including 180 distinct types of bacteria. Among the most scientifically significant finds were Moritella yayanosii and Shewanella benthica, both obligately barophilic organisms that require pressures of at least 50 megapascals to grow at all. S. benthica thrives optimally at 70 MPa while M. yayanosii prefers 80 MPa. Both species carry high concentrations of docosahexaenoic acid and eicosapentaenoic acid, omega-3 fatty acids that researchers believe could hold promise for treating hypertension and certain cancers. In May 1998, Kaikō collected specimens of Hirondellea gigas, a deep-sea amphipod crustacean, from the Challenger Deep. That same year's October mission near the Ryukyu Trench revealed Shewanella violacea at 5,110 meters, a bacterium distinguished by its vivid violet pigment. Compounds from S. violacea show potential in both the cosmetics industry for skin-lightening products and the semiconductor sector for manufacturing chemicals. These discoveries underscored how the deep ocean remains one of Earth's last great frontiers for bioprospecting.

Wrecks, Vents, and Robotic Prowess

Kaikō's operational record stretched well beyond biological sampling. In December 1997, the ROV located the wreck of the Tsushima Maru, a Japanese passenger and cargo vessel that had been sunk by the American submarine USS Bowfin during World War II. The ship had been unmarked, and its discovery off Okinawa offered a rare glimpse into wartime maritime losses. Just a few months later in late November of 1999, Kaikō found the debris of NASDA's H-2 No. 8 rocket resting at 2,900 meters near the Ogasawara Islands. That rocket had self-destructed shortly after its November 15, 1999 launch while carrying a Multi-Functional Transport Satellite payload. Kaikō also demonstrated impressive dexterity: in October 1999, it performed a robotic mechanical operation at 2,150 meters near the Ryukyu Trench, connecting measuring equipment to underwater cables on the sea floor. In August 2000, the vehicle discovered active hydrothermal vents and their associated deep-sea communities at 2,450 meters near the Central Indian Ridge, a divergent plate boundary between the African and Indo-Australian plates. These missions showcased Kaikō's versatility as both an archaeological and geological survey tool.

Loss, Successors, and Enduring Legacy

Kaikō's career ended abruptly on 29 May 2003, when Typhoon Chan-Hom battered the waters off Shikoku Island. A steel secondary cable that tethered the ROV to its surface launcher snapped under the storm's force, and the 10.6-ton vehicle was lost to the sea. JAMSTEC quickly moved to maintain its deep-sea research capability, deploying a converted ROV in May 2004 and later fielding Kaikō7000II as a dedicated replacement until 2007. By that year, sea trials had begun for ABISMO, the Automatic Bottom Inspection and Sampling Mobile vehicle, which would serve as the permanent successor. Throughout these transitions, the research vessel RV Kairei remained a constant, first supporting Kaikō, then Kaikō7000II, and now ABISMO. Kairei uses its ROV to survey oceanic plateaus, abyssal plains, submarine volcanoes, hydrothermal vents, and trenches to depths of 11,000 meters, and it also conducts multi-channel reflection surveys of complex subduction-zone geology. Kaikō's eight-year service life, though cut short by a single storm, established a template for unmanned deep-ocean exploration that its successors continue to build upon.