The Role Of Manned Submersibles In An Autonomous Age

The world’s oceans are increasingly active with sophisticated underwater technologies working to reveal long-hidden mysteries. However, sixty years ago, Denise was a pioneering and singular creation of its time.

Designed by Jacques-Yves Cousteau together with engineer Jean Mollard in 1959 at the French Centre for Undersea Research, Denise—also known as SP350—became the first crewed submersible built specifically for scientific study. By 1965, technological progress enabled Denise and Cousteau’s team aboard Calypso to reach depths of up to 500 meters and complete more than 1,500 dives. Six decades on, debate continues over whether human-occupied underwater systems still have a meaningful role in scientific exploration and what their future might be.

Autonomous systems have now become dominant in ocean research, driven by rapid advancements that have enabled entirely new capabilities. These include exploration beneath Arctic and Antarctic ice sheets and widespread adoption of Remotely Operated Vehicles (ROVs) in offshore energy industries such as oil and gas. Consequently, funding for many crewed submersible programs has declined, although specialists argue that human-piloted vehicles remain essential tools in marine science.

Carme Parareda, co-founder, administrator, and COO of ICTINEU Submarine SL, notes that despite the popularity of unmanned platforms, crewed submersibles continue to perform valuable work. She highlights systems such as Alvin, Shinkai 6500, Curasub, Undersea Hunter, Pisces IV and V, Deep Rover, and Jago as important contributors to marine research. She also observes that some scientists remain doubtful about crewed submersibles, viewing them as outdated—until they experience them firsthand, after which their perception often changes significantly.

Parareda explains that geologists were among the first scientific users of crewed submersibles. Later, the discovery of hydrothermal vents led to a surge in biological research using these vehicles, while in recent decades archaeologists have become particularly active users.

According to her, archaeologists value the precision these submersibles provide in delicate operations. Biologists benefit from direct visual access to deep-sea environments that far exceeds what camera systems on ROVs can deliver. Geologists, even after only a few dives, gain immediate three-dimensional understanding of seafloor structures, seamounts, and hydrothermal formations such as chimneys.

Dr. Adam Soule, Chief Scientist for Deep Submergence at the Woods Hole Oceanographic Institution (WHOI), similarly emphasizes the importance of human presence underwater. He argues that people can rapidly interpret complex three-dimensional environments, enabling efficient operations and high-quality sampling. He also notes that direct human experience in the deep sea is invaluable for training and inspiring future scientists and improving the use of robotic systems.

HURL’s Pisces submersible being deployed from a research vessel.

One example illustrating the transition between crewed and uncrewed systems is the Hawaii Undersea Research Laboratory (HURL). Established in 1981, HURL initially operated the manned submersible Makali‘i, which completed its first scientific dive in the crater formed by the first hydrogen bomb test at Enewetak Atoll. This marked the beginning of the program’s scientific diving operations after several months of fieldwork.

In 1986, HURL added Pisces V, followed by Pisces IV in 2000, acquired from the Canadian Navy. Both vehicles, designed originally for offshore industry applications such as cable surveying and burial, are capable of reaching around 2,000 meters. Their design includes skids that prevent direct contact with the seafloor, allowing them to straddle and work along underwater cables using water jets to create burial trenches.

HURL’s Pisces submersible inspecting a wreck near a Pacific atoll.

In 2005, HURL carried out an extensive expedition across 13 active volcanoes between Samoa and New Zealand. Although 56 dives were planned, the team successfully completed 63 despite difficult weather conditions. According to director of operations Terry Kerby, operating dual submersibles significantly increases both resilience and productivity, allowing simultaneous deployments on the seafloor.

As ocean exploration trends increasingly favor autonomous systems, crewed submersibles have faced institutional challenges. In 2012, NOAA ended funding support for Pisces operations, forcing the program to adopt smaller-scale operational strategies.

The team later revived the LRT-30a platform, which was re-certified and returned to service with a newly trained crew. A chartered support vessel enabled continued scientific dives, achieving a successful three-month field season. This flexibility allowed operations in extremely complex terrain, including shallow reef systems where tethered vehicles would struggle to operate safely due to entanglement risks or ship positioning constraints.

Inside the Alvin sphere, Bruce Strickrott and Susan Humphris. Photo credit: Chris Linder, WHOI.

Operational uncertainty continued through the mid-2010s. Funding proposals were rejected, while planned expeditions were repeatedly delayed or canceled due to geopolitical tensions and logistical challenges. Despite this, collaborations with government agencies, conservation organizations, and scientific institutions helped sustain intermittent missions and maintain operational capability.

Eventually, the Pisces systems were engaged in NSF-supported deep coral research missions in the Northwestern Hawaiian Islands. These expeditions involved extended field operations across multiple seamounts, though weather disruptions occasionally limited dive schedules.

Carme Parareda has remarked that although many researchers still view crewed submersibles as legacy systems, their usefulness becomes clear after direct experience.

A New Generation

Parareda also notes that operational costs have become a major concern, driving interest in alternatives to large ROV systems. While uncrewed platforms avoid onboard human risk, they can still suffer from loss or retrieval difficulties. In contrast, she argues that crewed submersibles currently offer a high level of operational safety and control.

Although ROVs and AUVs outperform in endurance and continuous operation time, modern vehicles such as ICTINEU 3 are narrowing the gap by enabling repeated long-duration dives with short recharge cycles, approaching robotic efficiency levels.

Crewed submersibles also offer advantages in complex environments, particularly where tethered systems risk entanglement.

Since 2004, ICTINEU Submarine has worked toward developing a new generation of human-occupied vehicles. Over time, advancements in engineering have addressed previous limitations in depth capability and design efficiency. Parareda explains that earlier research submersibles were extremely heavy, often requiring large support ships and heavy lifting equipment, similar to deep-water ROV systems. Reducing mass became essential to improve deployment efficiency and accessibility. ICTINEU 3, for example, weighs about 5.5 metric tons and carries three occupants to depths of around 1,200 meters.

Energy systems have also evolved significantly. Battery technology has progressed from older chemistries such as lead-acid and nickel-cadmium to modern high-energy lithium systems, along with experimental fuel cell approaches. ICTINEU engineers developed a high-density, pressure-compensated energy system that delivers significantly greater energy within similar volume constraints.

Hydrodynamic improvements have further enhanced safety, maneuverability, and efficiency. Future developments include intelligent piloting assistance systems inspired by aerospace technologies.

Parareda also points out that established platforms like Alvin have been upgraded, while new Chinese deep-sea vehicles such as Jiaolong and others are expanding capabilities.

Alvin

The Woods Hole Oceanographic Institution’s (WHOI) Human Occupied Vehicle program also reflects the evolution of deep-sea exploration. Commissioned in 1964, Alvin was among the earliest deep-ocean crewed submersibles. It was originally involved in recovery operations and later supported extensive scientific missions across diverse marine environments, including hydrothermal ridge systems and biological surveys.

In 1986, Alvin participated in exploration of the Titanic wreck site, producing iconic footage that later appeared in documentary and cinematic works.

Today, Alvin can reach depths of approximately 4,500 meters, granting access to a large portion of the ocean floor, with plans to extend its capability even further toward 6,500 meters, placing it among the few vehicles capable of reaching hadal environments.

Manned Submersibles and Citizen Science

The rise of citizen science has sparked interest in making deep-sea exploration more accessible, though debates continue regarding the suitability of crewed submersibles for public participation.

Soule notes that current crewed systems are primarily designed for expert scientific use, but advances in acoustic communication and data transmission are gradually enabling remote public engagement with deep-sea missions.

Stern view of Alvin during deployment on a research dive.

The Human Element

According to WHOI pilot Bruce Strickrott, crewed submersibles remain valuable because they complement other technologies rather than replace them. He emphasizes that direct human presence allows a depth of understanding that remote systems alone cannot fully replicate.

Parareda similarly argues that human involvement inspires public interest in ocean exploration in a way that autonomous systems cannot match, noting the emotional and educational impact of human exploration.

Soule concludes that rather than competing, manned and unmanned systems are most powerful when used together. He emphasizes that human immersion in the deep sea provides essential context for interpreting data and developing a deeper scientific understanding of marine environments.