Jacques Cousteau is remembered as an inventor and filmmaker, but his expeditions also produced real discoveries: he predicted porpoise echolocation in 1953, pioneered underwater archaeology at the Roman wreck of Mahdia (1948) and Grand Congloué (1952), helped develop deep-sea photography with MIT’s Harold Edgerton, proved Belize’s Great Blue Hole was a drowned cave (1971), and located the wreck of HMHS Britannic (1975).

Cousteau was not a laboratory scientist. His discoveries came from putting divers, cameras and instruments where nobody had been before, and from noticing things that specialists later confirmed.

Did Cousteau discover dolphin echolocation?

He predicted it. In The Silent World (1953), Cousteau described following porpoises through the Strait of Gibraltar and noticing that they seemed to know the best channel through the strait without seeing it. He concluded that cetaceans must have something like sonar. Echolocation in dolphins was confirmed experimentally by American researchers in the following years.

The passage is a neat piece of field reasoning. Aboard the naval sloop Élie Monnier, heading for the strait, the crew noticed porpoises riding alongside. Cousteau deliberately steered a few degrees away from the best course through the strait. The porpoises followed for a few minutes, then peeled away and returned to the mid-channel route, as if they knew where the deep, safe passage lay even when the ship did not. Since the water was too murky and the distances too great for vision alone, Cousteau suggested that the animals were navigating with something like the sonar that navies were then fitting to submarines.

Others were already working on the problem. The American psychologist Winthrop Kellogg recorded the clicks of captive bottlenose dolphins in Florida and in 1958 published “Echo ranging in the porpoise” in Science, showing that the animals could find their way around obstacles in the dark. In 1961 Kenneth Norris and colleagues produced the clinching evidence by fitting a dolphin with rubber suction-cup blindfolds and showing it could still navigate a maze of hanging pipes and find food by sound alone. Cousteau did not discover echolocation, but his book put the idea in front of millions of readers years before the experiments were done.

What did Cousteau find at the Mahdia wreck?

The Mahdia wreck was not new when Cousteau arrived. Greek sponge divers found it off the Tunisian coast in 1907, and between 1907 and 1913 the French archaeologist Alfred Merlin, then director of antiquities in Tunisia, directed helmet divers who raised bronze and marble sculptures, now in the Bardo Museum in Tunis. The ship, which sank between about 80 and 60 BC, was carrying Greek works of art, dozens of marble columns and furniture fittings, probably from Athens to Roman buyers in Italy. Among the finds are a bronze herm of Dionysus signed by the sculptor Boëthos of Chalcedon and a winged bronze youth identified as Agon or Eros, and lead ingots whose isotopes point to mines near Cartagena in Spain.

In 1948 Cousteau, Philippe Tailliez, Frédéric Dumas and their Navy diving group returned to the site aboard the Élie Monnier and dived it with Aqua-Lungs. The work was brief and far from a modern excavation, but it is often described as the first archaeological operation carried out with self-contained diving equipment. It showed that divers freed from air hoses and heavy helmets could move around an ancient wreck, examine it and film it, which changed what archaeologists thought possible underwater.

What happened at Grand Congloué?

Grand Congloué was a far bigger undertaking. A local diver, Gaston Cristianini, reported an ancient wreck beside a rocky islet near the island of Riou, just south of Marseille, in 1948. Cousteau began an excavation there in 1952 with the archaeologist Fernand Benoit as scientific director and Dumas as lead diver. The wreck lay at about 40 m, a depth at which air-breathing divers could manage only two or three dives a day and were vulnerable to nitrogen narcosis. To move sediment the team developed an archaeological suction dredge, an underwater “vacuum cleaner” lowered from a 25 m derrick erected on the rock. Over several seasons divers raised about 4,000 amphorae and some 10,000 fragments of pottery.

The project came at a cost. In November 1952 a young diver, Jean-Pierre Servanti, died on the site from the effects of narcosis, despite attempts by Albert Falco to save him. The scientific record was also flawed. Divers worked fast, and the site was treated as one ship; Benoit privately suspected otherwise but lacked the evidence. In 1980 a team from DRASSM, the French government’s underwater archaeology department, showed that two ships had sunk on the same spot about a century apart, their cargoes mixed together by the excavation. DRASSM itself had been created in 1966 by the culture minister André Malraux to put shipwreck research on a professional footing, in part because pioneering projects like Grand Congloué had shown both what divers could do and how much could be lost without trained archaeologists directing the work.

What shipwrecks did Cousteau discover or excavate?

The table mixes true discoveries with famous dives. Cousteau did not find Mahdia, and Grand Congloué was reported by a local diver; his team’s contribution was to work these sites with new equipment. The Thistlegorm, the Britannic and the Thérèse are closer to genuine finds.

Did Cousteau find the Thistlegorm?

Yes. The SS Thistlegorm, a British cargo steamer loaded with wartime supplies, was sunk by German bombers in the northern Red Sea in October 1941. In the early 1950s, following information from local fishermen, Cousteau’s team found the wreck and dived it from Calypso. They raised several items, including a motorcycle, the captain’s safe and the ship’s bell, and the February 1956 issue of National Geographic showed his divers inside the ship. Cousteau also described the dives in his book The Living Sea. Afterwards the wreck was largely forgotten except by fishermen, until the growth of diving at Sharm el-Sheikh in the early 1990s turned it into one of the most visited wreck dives in the world.

The Britannic, youngest sister of the Titanic and Olympic, was serving as a hospital ship when she struck a mine laid by the German submarine U-73 in the Kea Channel in the Aegean on 21 November 1916. She sank in 55 minutes; 30 of the 1,066 people on board died. Cousteau’s team found the wreck on 3 December 1975, lying on her starboard side at about 120 m, using sonar methods developed with Harold Edgerton. In 1976 his divers entered the wreck for the first time, and the expedition filmed interviews with survivors, including the nurse Sheila Mitchell. Cousteau believed the damage pointed to a torpedo; the mine explanation is now accepted. The ship remains the largest intact passenger liner on the seabed.

What was La Thérèse?

Thérèse was a 58-gun French ship of the line, built at Toulon between 1662 and 1665. In 1669 she was the flagship of a French expedition sent to help the Venetians defend Candia, today’s Heraklion in Crete, against a long Ottoman siege. On 24 July 1669, during a three-hour bombardment of Ottoman positions west of the city, her powder magazine exploded and she sank; only seven of about 350 crew survived. A Greek diver, Manolis Voutsalas, had found a wreck off the mouth of the Giofyros river but was unsure what it was. Cousteau’s dives in 1976 identified it as the Thérèse. From 1987 the Greek Ephorate of Underwater Antiquities carried out a proper excavation, recording about 30 m of surviving hull and raising objects including a bronze cannon inscribed “Le Duc de Vendôme 1666”.

How did Cousteau help photograph the deep sea?

In 1952 Cousteau met MIT engineer Harold “Doc” Edgerton, inventor of the electronic strobe. Their first joint expedition in 1953 off southern France produced the “pinger,” invented on the spot: a sonar device that triggered the camera and strobe when the rig neared the seafloor. Edgerton went on to design deep-sea cameras and sonar equipment for Cousteau’s expeditions for years, earning the nickname “Papa Flash”. His work was also instrumental in developing side-scan sonar, which sweeps a fan of sound sideways across the seabed and is now standard for finding wrecks; his company EG&G manufactured side-scan and sub-bottom profiling systems, and he took part in the search that located the Civil War ironclad USS Monitor.

What did Cousteau learn in the Blue Hole?

In 1971 Calypso charted the Great Blue Hole of Belize to about 125 m and found ledges at 21, 49 and 91 m. Divers retrieved stalactites from the walls, which can only form in air, proving the sinkhole was once a dry cave flooded by rising seas. Some were about 5° off vertical, all in the same direction, which suggested that the limestone platform itself had tilted after they formed.

The hole is about 318 m across, and later dating of stalactites from its caves suggested they formed during several periods of low sea level over the last 150,000 years or so, before the final flooding at the end of the last ice age. The 1971 expedition, filmed for The Undersea World of Jacques Cousteau, also turned the Blue Hole into a bucket-list dive; Cousteau ranked it among the best dive sites in the world.

The exploration Cousteau began is still going. In December 2018 two crewed submersibles descended into the hole and used sonar to build a near-complete three-dimensional map. They found a layer of hydrogen sulphide at about 90 m, below which the water is dark, anoxic and almost lifeless, a reminder that the “drowned cave” Calypso charted is also a chemically isolated pocket of the sea.

Where did the diving saucer take him?

Cousteau’s other route to discovery was the small submarine. With engineer Jean Mollard he developed the SP-350 “diving saucer”, a two-person submersible launched in 1959 and rated to 350 m, which could manoeuvre slowly over the seabed while its crew filmed through portholes. In 1963 it was housed in a hangar beside the Conshelf II habitat in the Red Sea, and in 1965 two smaller one-person vehicles reached 500 m. The saucer let Cousteau’s team film deep reef walls, canyons and the animals that live on them, at depths beyond the reach of compressed-air divers.

What did Conshelf discover about living underwater?

The Conshelf habitats (1962–65) showed that people could live and work for weeks at depth using saturation diving, from about 10 m in Conshelf I off Marseille in 1962, through a month-long stay at 10 m in the Red Sea in 1963, to 100 m in Conshelf III in 1965. That work fed directly into commercial saturation diving and later undersea labs such as Aquarius, home of Mission 31.

Conshelf II, in 1963, was the most ambitious. On the Sha’ab Rumi reef off Sudan, a team of oceanauts lived for a month in a starfish-shaped house at 10 m, while two of them spent a week in a “deep cabin” at about 30 m; a hangar on the reef sheltered the diving saucer. The men worked on the reef every day, underwent continual medical checks and showed that people could stay healthy and productive under pressure for weeks. Cousteau’s film of the project, World Without Sun, won the Academy Award for best documentary. Conshelf III in 1965 pushed the habitat down to about 100 m off Cap Ferrat, with six men breathing a helium-oxygen mixture. The petroleum industry had helped fund the work in the hope of permanent seabed stations; instead, remotely operated vehicles and surface-supplied saturation diving took over industrial tasks, and Cousteau turned away from seabed exploitation.

What else did Cousteau’s expeditions record?

Later voyages filmed Antarctica, including Deception Island in December 1972, where Calypso’s second-in-command Michel Laval was struck and killed by a helicopter rotor, the Amazon basin in the early 1980s, and the St Lawrence River and Great Lakes in 1980. These films documented ecosystems and threats rather than single discoveries.

How should we judge Cousteau as a discoverer?

Measured by formal scientific results, Cousteau’s record is modest. He was a naval officer and engineer, not a trained scientist, and he described few new phenomena himself. His real contribution was to make discovery possible for others: the Aqua-Lung freed divers from the surface; Calypso carried scientists and their instruments; the diving saucer, the underwater habitats and Edgerton’s cameras gave them access to depths and places no one had seen. Biologists, geologists and archaeologists who sailed with him published their own findings.

His early methods also attract criticism today. In the 1956 film The Silent World the crew used dynamite on a reef to count the fish it killed, slaughtered sharks that gathered around a whale carcass, and a whale calf was fatally injured by Calypso’s propeller. Grand Congloué showed what happens when excavation outruns archaeology. Cousteau himself changed. In 1960 he helped lead a public campaign that stopped the French atomic energy agency from dumping radioactive waste in the Mediterranean between Nice and Corsica, and by the 1970s he had turned against the industrial exploitation of the seabed he once promoted, and devoted the Cousteau Society, founded in 1973, to ocean conservation. Perhaps his most lasting discovery was that a television audience would care about the sea. That audience was built by The Undersea World of Jacques Cousteau and, before it, the Oscar-winning Silent World.