Crewed full ocean depth rated submersible
Limiting Factor, known as Bakunawa since its sale in 2022, is a crewed deep-submergence vehicle (DSV) manufactured by Triton Submarines and owned and operated since 2022 by Gabe Newell's Inkfish ocean-exploration research organization. It currently holds the records for the deepest crewed dives in all five oceans. 
"Limiting Factor" was commissioned by Victor Vescovo for $37 million and operated by his marine research organization, Caladan Oceanic, between 2018 and 2022. It is commercially certified by DNV for dives to full ocean depth, and is operated by a pilot, with facilities for an observer.
The vessel was used in the Five Deeps Expedition, becoming the first crewed submersible to reach the deepest point in all five oceans. Over 21 people have visited Challenger Deep, the deepest area on Earth, in the DSV. "Limiting Factor" was used to identify the wrecks of the destroyers at a depth of , and at , in the Philippine Trench, the deepest dives on wrecks. It has also been used for dives to the French submarine Minerve (S647) at about in the Mediterranean sea, and at about in the Atlantic.
Design and construction.
The submersible is based on a spherical titanium pressure hull for two occupants, seated side by side, which has three wide angle acrylic viewports in front of the crew, one in front of each seat, and one below and between them. If the bow is defined as the side in which the are mounted, the vessel is wider than it is long.
The vessel is equipped with a manipulator arm on the starboard side of the pressure hull, a system to drop ballast, and a cluster of five, fixed direction, ducted propeller, marine thrusters at each of the port and starboard ends of the outer hull for propulsion and maneuvering, as can be seen in the photographs. These thrusters provide three axis translational motion and two axis (yaw and roll) rotation.
The vessel is commercially certified for unlimited full ocean depth operations by DNV GL.
The "Limiting Factor" normally operates from a dedicated support vessel, , but can also be operated from other suitably equipped vessels.
Specifications.
Operational limits.
The designed operational maximum dive depth of represents approximate ;templatestyles src="Template:Visible anchor/styles.css" / ;full ocean depth – the maximum depth of the ocean of Earth. Test pressure of 14,000 msw ( fsw, ) provides a safety margin. The vessel has been certified to a preliminary maximum diving depth of by DNV, based on data from the deepest dive. The vessel is commercially rated for repeated dives to full ocean depth.
Principal dimensions.
The vessel is unusual in that it can travel on three primary axes, and in practice does a large amount of traveling vertically. If one uses the direction in which the occupants look out on the surroundings through physical windows to define the bow, it is wider than it is long. Alternatively it may be considered to have a bow at either end of the long axis, depending on the direction of motion at the time, like a proa. The long horizontal axis is , while the short horizontal axis extent is only . The height is .
Masses, weights and volumes.
The vessel is operated by a pilot, and has seating for an observer
Structure.
The pressure hull is a inside diameter by thick grade 5 titanium (Ti-6Al-4V ELI) alloy sphere machined to within 99.933% of spherical (for enhanced buckling stability). The sphere was built as two forged titanium domes that interlock with o-ring seals. The structure is certified for repeated dives to full ocean depth. The hydrodynamic fairing of the outer surface shell is non-structural and removable for access to equipment.
Power.
The vessel is operated from a dual 24 V battery power supply and emergency supply, which can be jettisoned in an emergency. The main battery stores 65 kW·h.
Propulsion.
There are 4 × horizontal propulsion thrusters (main thrusters), 4 × 5.5 kW vertical thrusters, and 2 × 5.5 kW maneuvering thrusters, mounted in two clusters at the opposite extremes of the long dimension. These can each be jettisoned if they become fouled on an obstruction, allowing the vessel to break free in an emergency.
Manipulator.
The DSV is fitted with a single Kraft Telerobotics "Raptor" hydraulically powered 7-function manipulator with force feedback, at the starboard side of the pressure hull.
Ergonomics, safety, and life support.
The forward and downward view through the three ultra-wide angle acrylic viewports is unobstructed by structure or appendages, and illuminated by ten externally mounted high output LED lighting panels of 20,000 lumens each. The limited direct field of view through the ports is augmented by an array of four full ocean depth capable low-light cameras. Four high definition cameras are also provided to record missions.
Maneuvering is by control joystick, touch screen and manual override.
The cabin is temperature and humidity controlled, and the life support system uses carbon dioxide scrubbers and oxygen replenishment. Emergency life support is rated for 96 hours.
All routine maintenance can be done using standard tools.
Emergency release systems are provided for the batteries, so they can be jettisoned if they fail dangerously, and for the thrusters and manipulator arm, in case they get snagged on an obstacle which could prevent the vessel from surfacing.
Deployment and recovery.
Launch and recovery from DSSV "Pressure Drop" is by a hydraulic luffing (tilting) A-frame over the transom. The vessel is stowed on deck in a cradle.
Name.
 ;templatestyles src="Template:Blockquote/styles.css" / ;The naming of these vessels is a large tip of the hat to, and with no small amount of admiration for, Iain M Banks' brilliant "Culture" science fiction series.
In Iain M. Banks' novel "The Player of Games", the General Offensive Unit (demilitarised) "Limiting Factor" is the sapient warship provided to the main character Jernau Morat Gurgeh for transport to the Empire of Azad to take part in a board game tournament. It is nominally demilitarised, but retains part of its main armament.
After the sale of the submersible to the research group Inkfish in 2022, it was renamed "Bakunawa" after the Filipino mythological creature Bakunawa.
Sale.
The DSV and support vessel DSSV "Pressure Drop" were sold in 2022 for an undisclosed amount to Gabe Newell's Inkfish ocean-exploration research organisation. The sale included a Kongsberg EM124 multibeam echo-sounder and three robot landers.
Inkfish plans to use the HES system to continue exploring the ocean depths, led by Prof Alan Jamieson of the University of Western Australia, who was chief scientist on most of Vescovo's expeditions.
The DSV was renamed to "Bakunawa" and the support vessel to "Dagon".
Expeditions as DSV "Limiting Factor".
Five Deeps Expedition.
In 2018, Victor Vescovo launched the Five Deeps Expedition, with the objective of visiting the deepest points of all five of the world's oceans, and mapping the vicinity, by the end of September 2019. This expedition was filmed in the documentary television series "Expedition Deep Ocean". This objective was achieved one month ahead of schedule, and the expedition's team carried out biological samplings and depth confirmations at each location. Besides the deepest points of the five world oceans, the expedition also made dives in the Horizon Deep and the Sirena Deep, and mapped the Diamantina fracture zone.
In December 2018, the "Limiting Factor" became the first piloted vessel to reach the deepest point of the Atlantic Ocean, below the ocean surface to the bottom of the Puerto Rico Trench, an area subsequently referred to by world media as Brownson Deep.
On 4 February 2019, Vescovo piloted "Limiting Factor" to the bottom of the South Sandwich Trench, the deepest part of the Southern Ocean, becoming the first person and first vessel to reach that point. In preparation for this dive, the expedition used a Kongsberg EM124 multibeam sonar system for accurate mapping of the trench.
On 16 April 2019, Vescovo piloted "Limiting Factor" to the bottom of the Sunda Trench south of Bali, Indonesia, reaching the deepest point of the Indian Ocean. The team reported sightings of what they believed to be previously unknown species, including a hadal snailfish and a gelatinous organism believed to be a stalked ascidian. The same dive was later undertaken by Patrick Lahey, President of Triton Submarines, and the expedition's chief scientist, Dr. Alan Jamieson. This dive was organised subsequent to the scanning of the Diamantina Fracture Zone using multibeam sonar, confirming that the Sunda Trench was deeper and settling the debate about where the deepest point in the Indian Ocean is.
On 28 April 2019, Vescovo descended nearly in "Limiting Factor" to the deepest place in the World – the Challenger Deep in the Pacific Ocean's Mariana Trench. On his first descent, he piloted the "DSV Limiting Factor" to a depth of , a world record by . Diving for a second time on 1 May, he became the first person to dive the Challenger Deep twice, finding "at least three new species of marine animals" and "some sort of plastic waste". Among the underwater creatures Vescovo encountered were a snailfish at and a spoon worm at nearly , the deepest level at which the species had ever been encountered.
On 7 May 2019, Vescovo and Jamieson, in "Limiting Factor", made the first human-occupied deep submersible dive to the bottom of the Sirena Deep, the third deepest point in the ocean, about northeast of Challenger Deep. They spent 176 minutes at the bottom, and among the samples they retrieved was a piece of mantle rock from the western slope of the Mariana Trench.
On 10 June 2019, Vescovo piloted "Limiting Factor" to the bottom of the Horizon Deep in the Tonga Trench, confirming that it is the second deepest point of the World ocean and the deepest in the Southern Hemisphere at . In doing so, Vescovo and "Limiting Factor" had descended to the first, second, and third deepest points in the ocean. Unlike the Sunda and Mariana Trenches, no signs of human contamination were found at Horizon Deep, which was described by the expedition as "completely pristine".
Vescovo completed the Five Deeps Expedition on 24 August 2019 when he piloted "Limiting Factor" to a depth of at the bottom of the Molloy Deep in the Arctic Ocean.
USS "Johnston".
USS "Johnston" (DD-557) was a built for the United States Navy during World War II. On 25 October 1944, while assigned as part of the escort to six escort carriers, "Johnston", two other "Fletcher"-class destroyers, and four destroyer escorts were engaged by a large Imperial Japanese Navy flotilla. In what became known as the Battle off Samar, "Johnston" and the other escort ships charged the Japanese ships to protect nearby US carriers and transport craft. After engaging several Japanese capital ships and a destroyer squadron, "Johnston" was sunk by gunfire, with 187 dead. The wreck was discovered on 30 October 2019 but was not properly identified until March 2021. Lying more than below the surface of the ocean, it was the deepest shipwreck ever surveyed until the discovery of on 22 June 2022.
On 30 October 2019, the , a research vessel belonging to Vulcan Inc., discovered the remains of what was believed to be "Johnston" near the bottom of the Philippine Trench. The remains consisted of a deck gun, a propeller shaft, and some miscellaneous debris that could not be used to identify the wreck, but additional debris was observed lying deeper than the ship's ROV could go. On 31 March 2021, the "Limiting Factor" piloted by Victor Vescovo, surveyed and photographed the deeper wreckage and definitively identified it as "Johnston". The wreck lies upright and is well preserved at a depth of . Until "Samuel B. Roberts" was discovered on 22 June 2022, "Johnston" was the deepest identified shipwreck in the world.
USS "Samuel B. Roberts".
USS "Samuel B. Roberts" (DE-413) was a destroyer escort of the United States Navy that served in World War II and was sunk in the Battle off Samar, in which a small force of U.S. warships prevented a superior Imperial Japanese Navy force from attacking the amphibious invasion fleet off the Philippine island of Leyte. The ship was part of a relatively light flotilla of destroyers, destroyer escorts, and escort carriers called "Taffy 3" which was inadvertently left to fend off a fleet of heavily armed Japanese battleships, cruisers, and destroyers off the island of Samar during the Battle off Samar, one of the engagements making up the larger Battle of Leyte Gulf of October 1944. Steaming through incoming shells, "Samuel B. Roberts" scored one torpedo hit and several shell hits on larger enemy warships before she was sunk. As of June 2022,