Alvin and the ROVs

Despite having traveled over its surface for millenia, man still knows relatively little about the deepest depths and middle regions of the sea. In fact, it's probably fair to say that man knows more about many regions of outer space. One reason for this is the tremendous pressures that exist in the deep sea. Nonetheless, a brave handful of tiny steel-hulled vessels have ventured forth into the abyss and brought forth a wealth of information on geological, chemical, physical, and biological processes within the ocean. In this lecture, we survey some of these vessels and look towards the future of undersea exploration as new technology emerges.

Why Investigate the Deep Sea?

For centuries it was thought that the bottom of the ocean was a vast, lifeless desert. Devoid of anything of commercial value, the ocean depths were left unexplored until the advent of technologies that made use of the ocean floor. One of these technologies was the telephone which required that placement of thousands of miles of cables across the sea to enable communications between America and Europe.

Early cable laying expeditions encountered a number of problems. It was soon discovered that the ocean floor wasn't flat. Furthermore, cable was subject to breaking, both by the forces of turbidity currents and by the actions of marine organisms that "weren't supposed to be there." These early enterprises revealed much of the deep sea and highlighted a need to understand more about the ocean floor.

Another compelling interest in the ocean floor arose as a result of submarine warfare during the second World War. The invention of sonar and the realization that several prominent features of the ocean floor made good hiding places led to an further investigations of sea floor bathymetry.

As mentioned previously, investigations of the seafloor in the 1950s and 60s accelerated the confirmation of the theory of plate tectonics, as proposed by Alfred Wegener decades earlier. These geophysical investigations of the deep sea and man's advances into outer space spurred the development of vehicles that could take man to the bottom of the sea. In 1965, the American submersible Alvin was launched, which completed its first sucessful mission recovering a lost H-bomb in the Mediterranean off the coast of Spain. Subsequent missions by Alvin and other submersibles revealed the striking rift valleys of mid-ocean ridges and uncovered heretofore unknown forms of life.

Given the vast terrain which the ocean floor covers and the incredibly small percentage that we have explored, there are many compelling reasons to investigate the deep sea. The advent of inexpensive unmanned vehicles, such as Remotely Operated Vehicles, or ROVs, and Autonomous Underwater Vehicles, or AUVs, are sure to stimulate increased exploration of this fascinating and forbidding "corner" of the earth. As man delves deeper into the abyss, it is likely that many new and strange forms of life will be revealed. Who knows what lurks beneath the dark and intrepid sea?

The Story of Alvin

Believe it or not, the American submersible Alvin was named after the famous cartoon chipmunk. The operational team who built the craft coined the name partly after the cartoon character but also in reference to their boss and Alvin's chief supporter, Allyn Vine, of the Woods Hole Oceanographic Institute. Despite efforts to find a more proper name, the slang stuck and Alvin etched a name in oceanographic history that will be remembered through all time.

Alvin was built by General Mills at a cost of $472, 517. Following completion of sea trials, the submersible was put into the water on June 5, 1964, and in 1965, completed its first manned 6,000-foot dive.

Highlights of Alvin's service record are summarized below, as provided by the Woods Hole Oceanographic Institution Web Site on Alvin. Notable events include the 1967 attack on Alvin by a swordfish; the 1968 "loss" of Alvin on the seafloor; the 1969 recovery of Alvin and the discovery of "edible" sandwiches; Project FAMOUS in 1974, which revealed the structure of the mid-Atlantic Ridge for the first time; the 1977 discovery of hydrothermal vent organisms in the Galapagos Rift; the completion of its 1000th dive in 1980; the discovery of cold water vent communities in the Gulf of Mexico in 1984; dives on Loihi in 1987; dives in the Santa Catalina basin off San Diego in 1988; recovery of a Navy ROV off the coast of southern California in 1991; Alvin's 30th birthday on June 5, 1994; and Alvin's 3000th dive on September 20, 1995.

1966

An Air Force B-52 and a tanker collided over Spain, dropping an H-bomb in the Mediterranean off Palomares, Spain, in January. The ALVIN team was selected to attempt recovery. In February 1966, ALVIN and its support vans were loaded into two Air Force cargo aircraft at Otis Air Force Base and flown to Rota, Spain. During the next two months, ALVIN, operating from a Navy LSD, searched the ocean floor off Spain for the lost H-bomb. The bomb was located for the first time on March 15, but was subsequently lost during an attempt to attach lift lines. The bomb slid down-slope to deeper water, and the search continued. The bomb was relocated on April 2 and recovered April 7. ALVIN returned to Cape Cod for completion of the overhaul begun before the Spanish adventure.

1967

ALVIN returned to the Bahamas for Navy dives with subsequent transit north for biology/geology dives on the Blake Plateau and off Cape Charles. During Dive 202, on July 6, ALVIN was attacked by a swordfish on the bottom at about 2,000 feet. The fish became trapped in ALVIN's skin and was brought back to the surface (and cooked for dinner).

ALVIN completed a series of dives south of New England in the canyons and along the continental slope for geology, biology, thermal studies and sound measurements. On Dive 209, in the Hydrographer Canyon area, a Navy F6F aircraft was found, photographed, and surveyed. It was later identified as being lost overboard from a carrier during practice runs in 1944 (the pilot escaped).

On Dive 224, September 24, the mechanical arm was lost during a rough recovery. The arm was subsequently found and recovered on dive 236 on October 15. It was reconditioned and reinstalled.

1968

A series of dives were made to look for submerged whales, Navy dives surveyed the tops of seamounts for a new acoustic test range and geology and biology studies were completed. During the launch for Dive 308 on October 16, ALVIN's cradle support cables failed and ALVIN slid into the water and sank to the bottom in 5,000 feet of water. Ed Bland, pilot, received some bruises and a sprained ankle while exiting from the sub. Poor weather conditions and insufficient recovery equipment prevented recovery during the remainder of the year.

1969

ALVIN remained on the bottom until Labor Day. The DSV ALUMINAUT (a submersible from the Reynolds Aluminum Company) and the R/V MIZAR assisted in the recovery, which required placement of a lifting bar into ALVIN's hatch (ALUMINAUT pilots had to break the sail in order to accomplish this). MIZAR then raised ALVIN to 50 feet, where divers wrapped the sub with lines and nets to prevent loss of any pieces. ALVIN was towed to Martha's Vineyard, where a crane mounted on a barge pulled it out of the water. Overall, there was very little structural damage to the submersible (except for the sail). Lunches left on board were soggy but edible. Discovery that near-freezing temperatures and the lack of decaying oxygen at depth aided preservation opened up new areas of biological and chemical research.

1970

ALVIN underwent a major overhaul after its ten-month dunking.

1971

ALVIN's first post-loss dive was 309 on May 17. In mid-June a permanent bottom station was established on the continental slope south of Martha's Vineyard. The station was regularly revisited for many years. When Ruth Turner visited the bottom station on Dive 345, it was the first science dive with a woman observer.

The Gulf of Maine and the Straits of Florida provided sites for the next series of dives. On Dive 364 ALVIN was attacked and hit by a large blue marlin while on the bottom off Grand Bahama Island. The fish did some damage to the underwater lights and sail and much damage to himself.

1972

A series of dives were completed for biology at the Martha's Vineyard station, for geology and biology in the Hudson Canyon, and in the Gulf of Maine (geology) for navigational and rock drill experiments.

1973

During the spring, a new titanium pressure hull and variable ballast system were installed. After a series of simulated dives in a Maryland pressure test tank, ALVIN was officially certified to 12,000 feet.

1974

Project FAMOUS (French-American Mid-Ocean Undersea Study) provided our first close-up look at the Mid-Atlantic Ridge along with the French submersibles CYANA and ARCHIMEDE. National Geographic ran articles on the Project in the May 1975 issue, authored by WHOI scientists Bob Ballard and Jim Heirtzler.

1975

ALVIN completed a series of dives in the Bahamas (biology), at Grand Bahama Island (geology), Blake Plateau (biology), and made a radioactive waste dump site survey. A new deep (12,000 feet) bottom station south of Cape Cod was established.

1976

ALVIN was certified for 4,000 meters (13,124 feet). A series of geology dives took the sub to the Cayman Trough, and Navy dives were made near St. Croix and Tongue of the Ocean. Biology studies were carried out on the shelf, slope, and canyons south of Cape Cod. A waste drum was recovered from the radioactive waste disposal site off New Jersey.

1977

ALVIN traveled through the Panama Canal for the first time. Geology work in the Galapagos Rift was completed during February and March. The major discovery of an abundance of exotic animal life on and in the immediate proximity of warm water vents prompted theories about the generation of life. Since no light can penetrate through the deep waters, scientists concluded that the animal chemistry here is based on chemosynthesis, not photosynthesis.

Return passage was made through the Canal for April dives in the Cayman Trough (a continuation of a geology investigation). During this series a Nicaraguan earthquake occurred and was plainly felt by ALVIN while submerged.

1978

A new titanium structural frame was installed. Radioactive waste and biology studies continued off the East Coast. A second trip to the Mid-Atlantic Ridge was made for plate tectonic (geology) studies at the spreading center.

1979

Transit to Panama was followed by biology and geology cruises to the Galapagos in January and February. National Geographic filmed dives for the highly acclaimed special "Dive to the Edge of Creation."

In April and May ALVIN made its first trip to the East Pacific Rise at 21 deg North. These geology dives revealed hot water vents or "black smokers" spewing forth super-heated water at 350 degC (650 degF). Many of the same animals found at the Galapagos vents were found at this location off Mexico. Further dives near San Diego, Tamayo Fracture Zone, East Pacific Rise, and Galapagos were made from June through December.

 1980

ALVIN completed its 1,000th dive at the Galapagos Rift in January.

ALVIN returned to the Mid-Atlantic Ridge and Kane and Oceanographer Fracture Zones during June and July for geology studies as well as additional dives along the East Coast, the Bahamas, and St. Croix. The BBC filmed a television special.

1981

Extensive work continued in the St. Croix area, after which ALVIN returned to Galapagos and the East Pacific Rise following dives in the Panama Basin.

1982

The schedule included dives at East Pacific Rise and Guaymas Basin. CBS News Anchor Walter Cronkite made Dive 1211 to the hot vents. Dives at the Panama basin were followed by a long transit to the Mid-Atlantic Ridge. ALVIN returned to Woods Hole in August and completed local studies for biology, geology, and ocean engineering followed by dives in the Florida Straits and the Providence Channel.

1983

A major ALVIN overhaul in Woods Hole included the addition of a T-fitting on the sub's frame to allow for a single-point overhead lift system, replacing the elevator method. At the same time, R/V ATLANTIS II was prepared for its new role as mother ship and tender for ALVIN. These extensive modifications were conducted during AII's regular mid-life refit. A large A-frame was added to the stern for ALVIN launch and recovery.

1984

ALVIN and ATLANTIS II departed Woods Hole in January for Charleston, SC. Final preparations and harbor tests, including the first actual ALVIN launch and recovery with the A-frame, were followed by a geology cruise to the Blake Plateau. Several rough water recoveries were made at sea, proving the A-frame system could work under less than ideal conditions.

During a March geology/biology cruise on the West Florida Escarpment in the Gulf of Mexico, a series of bottom cold water vent communities were discovered. The animals found were very similar in appearance to those in the Pacific.

ALVIN transited to the Pacific for further dives in the Panama Basin and on the East Pacific Rise. In mid-April the towed camera sled ANGUS discovered a new vent field to the south of the dive area, and ALVIN visited it.

Dives at the Juan de Fuca and Gorda Ridge off the coasts of Oregon and Washington in July revealed black smoker hydrothermal vent activity in this northern spreading center.

1985

Much of ALVIN's work during 1985 focused on the vent communities at Guaymas Basin in the Gulf of California, the East Pacific Rise off Mexico, and near the Galapagos Islands. Successful tests were made of new deep ocean sampling and photographic equipment designed for control from within ALVIN. In November, ALVIN returned to Woods Hole to begin a five-month overhaul.

1986

The first part of the year was spent completing the major overhaul, with improvements made to the submersible's propulsion, electrical, and instrumentation systems. The large stern and small side lift propellers were replaced by six small electric thrusters to increase speed and maneuverability. Brushless DC motors designed specifically for ALVIN replaced the hydraulic propulsion system, providing increased reliability, efficiency, and performance.

Other improvements were made to ALVIN during the overhaul. Safety release devices, payload capability, personnel sphere internal arrangement and the data logging/display system were upgraded.

In May, certification dives were held in Bermuda before ALVIN returned to service. Dives on the Mid-Atlantic Ridge at newly-found hot water vents discovered new species of shrimp and a six-sided animal thought to be extinct. In July, considerable media attention focused on dives to the wreck of RMS TITANIC. ALVIN made 12 dives to test a prototype robotic vehicle called Jason Jr. and to photographically document the wreck. After several other cruises in the North Atlantic, ALVIN departed Woods Hole in late September to begin a two-year voyage into the Pacific. Year-end dives were made in the eastern Pacific with a holiday port call in San Diego.

1987

Short cruises in the Santa Catalina Basin in early January were followed by a series of dives on Loihi Seamount, south of the Hawaiian Island chain, as scientists studied the underwater volcano which will eventually be a new Hawaiian island.

Dives in the western Pacific near the Mariana Islands kept ALVIN busy for much of the spring and summer, with new hydrothermal vent communities discovered in that area. A port call in Tokyo in early August brought thousands of visitors, including Japan's Crown Prince Akihito. Transit to Oregon followed as ALVIN began a series of dives on the Juan de Fuca Ridge off Washington and Oregon to continue ocean floor studies. Year-end dives in the Santa Catalina Basin were followed in November by drydocking of ATLANTIS II in San Diego for routine hull repair and maintenance.

1988

Biology dives in the Santa Catalina Basin off San Diego in January preceded extensive biological and chemical studies in the Guaymas Basin. A trip to the East Pacific Rise in March saw geological work on ridge processes and was the site of ALVIN Dive 2000 on March 22nd. ATLANTIS II and ALVIN headed farther south in April to the Galapagos area for more research at the vent sites first explored in the mid-1970's. A series of dives on the Oregon Continental Margin and Juan de Fuca Ridge began in early June to measure geological and geochemical processes as well as heat flow rates at "hot smoker" locations. In October, a benthic drifting algae and geologic study was conducted in Monterey Canyon, followed by more dives in Catalina Basin. In late November, the ship and submersible visited a biological study site at an underwater volcano off Acapulco, then transited the Panama Canal en route to Woods Hole.

1989

The first seven months of 1989 saw ALVIN undergo its triennial overhaul, with replacement of the sub's through-hull electrical penetrators the major task. ATLANTIS II, meanwhile, carried scientists to the Mid-Atlantic Ridge for the first nonsubmersible studies since the 1983 conversion. A series of test and certification dives near Bermuda started the diving research season in mid-August, followed by work on the continental rise off New Jersey and biological community studies at the New York Bight sludge dumpsite. ALVIN started December with more geological sampling on the rise south of New England, and following the holidays departed on Leg 1 of Voyage 125, scheduled to keep the ship operating away from Woods Hole for almost three years.

1990

The first score of dives this year was spent exploring geochemical aspects of active hydrothermal vents on the Mid-Atlantic Ridge south of the Azores. After transiting to Jacksonville, ATLANTIS II entered the shipyard for a month of maintenance concurrent with minor ALVIN upkeep.

In mid-March the submersible resumed diving in the Gulf of Mexico, visiting hydrocarbon seeps, brine pools and abyssal basins to catalog new biological species. Following transit through the Panama Canal, the vessels stopped briefly in Costa Rica to embark scientists before conducting geological structure measurements in the Hess Deep Rift Valley west of the Galapagos. The next port stop was Guayaquil, Ecuador, before diving continued at the Galapagos Rift, East Pacific Rise and Guaymas Basin.

Transiting north in July, ALVIN began work on the Juan de Fuca Ridge in support of geophysical crustal studies, followed by interdisciplinary work for NOAA on the southern end of the ridge in August. The ship worked its way back south during September, with dives in Monterey Canyon en route to San Diego. Twin dive series on Fieberling Seamount west of California occupied the majority of the fall, while short cruises to the Santa Catalina Basin in early and late November allowed studies of benthic biology and ALVIN's Navy inspection.

1991

The diving season opened in February in the Santa Catalina Basin where studies of whale bone biological communities were conducted. Following a transit to the Gulf of California, diving continued in the Guaymas Basin in support of hydrothermal vent system experiments. From there the ship and submersible returned to the East Pacific Rise for two studies of hydrothermal, volcanological and geochemical processes near ODP drill sites and the Siqueiros Transform. After transit back to San Diego in late May, ALVIN entered a maintenance period in which the main batteries were replaced and a Navy certification audit was successfully completed.

One week prior to the end of the maintenance period the ALVIN Group was requested to assist the Navy in the recovery of its CURV III towed ROV system, lost off the coast of southern California. ALVIN was quickly reassembled and made four search dives before finally recovering the vehicle on July 1st.

Following the recovery, the ship headed north to Oregon to begin a season of operations on the Juan de Fuca Ridge. The first cruise supported the initial stage of interdisciplinary studies of hydrothermal flange evolution, followed by biological examination of mollusc populations. A NOAA Vents Program cruise followed, featuring chemical and geological work on the southern ridge. During a second hydrothermal flange cruise in early September five auxiliary dives were conducted to support Office of Naval Technology experiments and to obtain data and samples from a previously instrumented Ocean Drilling Program (ODP) bore hole. The last Ridge leg of the year revisited the northern vent sites for isotope experiments and also revisited the ODP site for maintenance of the bore hole instrumentation.

After a month-long shipyard overhaul of ATLANTIS II, the final cruise of the 1991 dive year visited the East Pacific Rise for plankton studies in hydrothermal vent plumes.

1992

Our first cruise in early February gave the ALVIN Operations team a rare chance to conduct a series of engineering test dives off San Diego. Experts in the photographic, underwater video and acoustic fields were invited to participate in five shallow dives to recommend improvements in ALVIN's capabilities. Experiments included calibration of the still camera fields of view, evaluation of a new generation of video lighting and qualitative analysis of optimum light configurations, exposure tests for various cameras, application testing of a low-cost fathometer, and vehicle attitude/performance analysis. Extensive testing of the sub's hydraulic system resulted in corrective measures designed to bring performance up to advertised capability. Constructive external input from industry participants has already fostered interest in both real-time, 3-D graphical display of ALVIN's position in a navigated volume and the potential for "video inertial navigation" from computer processing of video images.

Scientific dives began on the East Pacific Rise in late February, where a multi-institutional team of investigators studied hydrothermal and geochemical processes in support of ODP work. The Rise area at 9 deg N had been found to be active during a late-1991 dive series, so experiments during this cruise provided an unusual temporal look at vent processes. Late in March, the Rise at 21 deg N was the site of geochemical sampling of hydrothermal fields, and in April scientists returned to the Rise at 10 deg N to complete experiments initiated with the French submersible NAUTILE in 1991.

Following a transit through the Panama Canal in early May, ALVIN and ATLANTIS II made a port call in Galveston before beginning studies of chemosynthetic ecosystems at two sites in the Gulf of Mexico. Two dives were made for specimen collection at the West Florida Escarpment cold seeps, and the final dive of Voyage 125 allowed a video transect of megafaunal habitats on the Continental Rise near Block Canyon. The ship and sub returned to Woods Hole on June 10th after 575 days at sea, 367 dives and 894 days away from home port.

After a six-week layup the vessels departed WHOI in early August for studies of biological communities at Deepwater Dumpsite 106 off New York. Upon return to Woods Hole mid-month, ALVIN began a major overhaul period.

1993

The overhaul period ended in mid-March with certification and engineering dives off Bermuda. Two subsequent dives for the Royal Ontario Museum and the Bermuda Zoological Society sought to catalog biodiversity and biota zonation on the flanks of the island pedestal and nearby seamounts. We next embarked on a seismic studies cruise to the Mid-Atlantic Ridge, but mechanical/electrical problems with ALVIN's new pressure-tolerant motor controllers resulted in a radically shortened dive program. Repairs were effected during a maintenance period in Bermuda in April, after which the sub successfully completed three dive series back at the ridge, including work at a newly-discovered vent field south of the Azores. One Deep Water Dumpsite revisit cruise was undertaken in mid-July before the now-familiar transit through the Canal to the Pacific study areas. Fall explorations on the Juan de Fuca Ridge focussed on geomorphology, geochemistry and the retrieval of data from instruments left on ODP well holes. In October ALVIN's schedule was modified to include a cruise to the Axial Seamount area to investigate recent volcanic eruptions in the hydrothermal vent field; use of the former Navy underwater early-detection acoustic system had alerted scientists to possible activity. Evidence of new formations was indeed found at the site, proving the validity of this new tool for event detection.

A shipyard period in November preceded the final voyage of the year, to the East Pacific Rise in support of biological community temporal studies.

1994

This year began as the last one ended, with four lengthy cruises to the East Pacific Rise and Costa Rica Accretionary Wedge. Most of the work was in pursuit of geological and biological programs, with an added dive for salvage purposes: a lost University of Washington rock drill was recovered in late January.

Two milestones were reached this year, the first in early February. An arduous series of calculations and tests, performed in conjunction with the NAVSEA branch of the Navy, had proved that ALVIN's pressure hull was capable of withstanding even greater pressures than it had yet been subjected to, while still maintaining the substantial safety factor required for human occupancy. An increase in our depth rating by as little as 500 meters (to 4,500 meters or 14,764 feet) would allow investigators to explore an additional 20% of the ocean bottom! Replacement of the steel motor controller housings would be required due to their insufficient thickness, but once new titanium units had been installed the path was cleared to recertification. On February 5 three ALVIN pilots made the historic dive to our new depth limit, paving the way for additional deep dives during the Costa Rica voyage.

The second date of note was June 5, 1994: ALVIN's 30th birthday. Most frequently asked question during the ceremonies held at Woods Hole and attended by numerous military and governmental dignitaries: does any part of the original ALVIN remain in use today? The answer: no, all parts of the sub have been replaced at one point or another during her illustrious career as a deep ocean research platform, including the frame and pressure hull.

As with many government-funded operations in the US of late, the ALVIN program was required to yield to budget pressures and curtail work by 60 days this year. A 30-day stand down in May was followed by a return to the Juan de Fuca area, where scientists continued time series measurements at hydrothermal vent field sites. A crew from a nature films production company recorded dives on the northern Ridge for inclusion in a television special on underwater research. In late summer-early fall a team from Scripps Institute of Oceanography studied benthic boundary layer biological communities at a site off California, followed by three final cruises to the Guaymas Basin and East Pacific Rise. A new, submersible-mounted rock drill was successfully tested, retrieving samples of volcanic material previously unreachable. 1994 ended with a transit to and the final half of the mandated stand down in Woods Hole.

1995

The first voyage of the year took ship and submersible back to the TAG hydrothermal site on the Mid-Atlantic Ridge to complete dives lost two years earlier because of motor controller problems. The next leg visited an ODP well site to collect data from emplaced instruments, followed by a transit through the canal and on to the bottom station at 9 deg N on the EPR, where the progress and growth of biological communities were cataloged. Working their way up the Latin American coast, investigators stopped off California for more biology studies, then proceeded on to the Juan de Fuca for a very full season (81 dives) of multi-disciplinary work. Most programs were continuations of previous field research, but new cameras, sonar systems and other sensors recently added to the sub allowed new looks at vent features and fauna. Laser range finders mounted on the sponson now permit scientists to measure the size of objects in the still and video camera fields of view, and vastly improved lighting facilitates close-up observation. ALVIN's two hydraulic manipulators can reach and retrieve artifacts on the bottom, and also activate a variety of water and sediment samplers developed for deep sea use.

ALVIN recorded Dive 3000 on September 20. A live underwater telephone/satellite link allowed shoreside dignitaries to congratulate the pilot and observers during the dive.

Alvin Dive Statistics: 1964-1996

Total Dives

3,096
Total Depth (meters) 6,266,006
Average Depth per Dive (meters): 2,024
Total Time Submerged (hrs): 20,734
Average Time Submerged per Dive (hrs): 6.70
Total Persons Carried: 9,288

ROVs, AUVs, and Luxury Submarines

A short article from the May 1995 Special Issue of Popular Science provides an excellent overview of Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs). A copy of the article is available for your review.

You may recall that an ROV named Jason helped discover the whereabouts of the Titanic. Hundreds of ROVs have been put to work in the sea, primarily because they can accomplish tasks for less expense and with less risk than manned vehicles. ROVs are commonly used around oil platforms and for laying underwater cables. They come in all shapes and sizes and may be equipped with any number of special gizmos for performing underwater tasks, such as rock cutting, trench digging, sample collecting, or just plain videotaping.

ROVs are tethered to either a ship or a submerged platform. Because they are attached to a ship, all of their power and communication needs can be met through the conducting cable. However, the cable places restrictions of where the ROV can operate (it's difficult to guide an ROV through the hull of a ship) and it's hard to use one in bad weather when the ship is being dashed about. Nonetheless, ROVs are the most reliable and least expensive of the underwater vehicles, which is one reason why they are so popular.

AUVs have the luxury of going where they want in the ocean. One principal use of an AUV is in search-and-recovery operations for ships or aircraft downed at sea. Because they are independent, they require an internal energy source and they must have some means of sotring the information they gather. Furthermore, AUVs need to be quite a bit "smarter" than ROVs; they need to be able to make decisions as to whether an object they locate fits the "description" of the object they are looking for. More than one AUVs have impaled themselves on the superstructure of some ship as they attempted to accomplish their mission. The other problem with an AUV is that they may not return. As with any computer-operated machinery, an endless loop of some kind can literally put the AUV in an endless loop until it expires all of its energy and sinks to the bottom of the sea. Nonetheless, advances in artificial intelligence and computer technology are bringing AUVs to the forefront as a useful and practical solution to many ocean-related problems.