Slicing through tropical reefs or patrolling Arctic waters, the Calypso gained worldwide fame as the research ship of the French underwater explorer Jacques-Yves Cousteau. Seen by millions on TV documentaries broadcast worldwide, the Calypso helped Cousteau and his team show the world never-before-seen underwater wonders and raise awareness of environmental issues.

The Calypso, then known only as BYMS-26, was launched in Seattle, Washington, in 1942. The ship served admirably as a minesweeper in the British Royal Navy during WWII under the designation J-826. After the war, the ship endured a less-than-glamorous stint ferrying passengers and cars between Malta and Gozo. At least it received a new name: Calypso, after the figure in Greek mythology who kept the shipwrecked hero Odysseus enraptured for seven years with vague promises of immortality.

Cousteau, who was then serving in the French navy, had already gained fame as the co-inventor of the Aqua-Lung and as an underwater explorer, but by 1950, he wanted to bring the marvels of the sea into people's living rooms. To do that, he needed a ship. The navy refused to offer one, and Cousteau could not raise the funds to buy one. Then a miracle happened. After only his second meeting with Cousteau, Loël Guinness, a member of the super-wealthy brewery family, decided to help. Guinness told Cousteau to find himself a suitable vessel, and he would put the money up for it. Cousteau visited Malta and chose the Calypso, but he had no idea how he could ever repay the loan. In fact, he did not need to. Guinness generously leased the ship to Cousteau for a mere £1 a year. The fantastic offer came with two conditions. Cousteau could not tell anyone except his wife about the deal, and he could never ask Guinness for money again.

Cousteau, given three years leave from the navy, sailed the Calypso to Antibes in southern France and set about converting the ship into a state-of-the-art floating oceanographic institute with radar, sonar, laboratories for the study of marine life, a machine shop for equipment repairs, a freezer room for specimens, and its own photographic studio. The refit cost some serious money, cash that Cousteau still did not have. Cousteau was obliged to mortgage his house, sell his wife's jewellery, and like many other terrestrial explorers before him, beg from rich people. Generous donations did come in, and there was, too, hope of future royalties from television and books of the expeditions Cousteau planned to make. Cousteau was canny enough to realise that film and science could be a perfect match if presented in the right way. The idea would revolutionise both exploratory science and prime-time television.

Relatively small at 139 feet (42 m) in length, the Calypso's hull of tough and virtually rotproof cedar could cut through waters ranging from the tropics of the Indian Ocean to the ice floes of Antarctica to the mighty Amazon River. The ship handled superbly and had a shallow draft, which meant it could go almost anywhere. Another plus was the boat's low afterdeck, which was ideal for use as a divers' platform. Cousteau even cut a square hole in the ship's hull so that divers could descend directly into the sea in foul weather using a ladder.

The tough old ship provided a home for a crew of around 30 and was fitted with a helicopter and landing pad. A crane could gently drop a submersible, what Cousteau called his 'diving saucer', into the sea. The ship could even launch a hot-air balloon for superior aerial photography. Besides its laboratories and high-tech equipment, perhaps the Calypso's most stunning adaptation to its role as investigator of the seven seas was a false bow section with an underwater observation chamber where a camera operator could lie on a mattress and film unique shots of passing marine life. Finally, the ship's funnel was painted with a new insignia, a green and white sea nymph and dolphin with the word 'Calypso' beneath.

Setting off to explore the world's oceans in 1951, the Calypso would serve Cousteau well for over 40 years. The Frenchman made a long series of TV films and documentaries in the 1960s, '70s, and '80s, which gripped viewers worldwide. One of the stars of shows like The Silent World (which won an Oscar), The Undersea World of Jacques Cousteau, and The Cousteau Odyssey was the Calypso, usually featured heavily in the opening credits and throughout the programmes. Viewers saw all the ship's latest gadgets but also came to realise it was a much-loved safe haven for the divers after long hours under the sea. The ship was a place for camaraderie, particularly in the mess room where 'Captain' Cousteau held sway. All of the 22 divers could squeeze around the mess table, eat fish stew, discuss the day's work, and pore over charts weighted down with bottles of wine (Calypso had its own wine cellar). Cousteau had indeed built a cosy home as he lived the life of a permanent explorer with his wife on board (but rarely seen on film) and two young sons registered as cabin boys. Signing up to work on Calypso required a particular kind of dedication. As Cousteau once remarked:

I cannot help thinking that the men of Calypso resemble, in many ways, those of Jules Verne's Nautilus – men who have been wounded by life on land, and who thereafter put their trust in the sea.

The Calypso enabled Cousteau's team of scientists and divers to discover new species, film for the first time denizens of the deep, rescue artefacts from ancient shipwrecks, and educate the world about just what went on under the surface of the sea. Cousteau's all-action programmes dramatically changed the way science programmes presented the natural world, and he was one of the first to warn how the delicate balance of ocean life was under threat from environmental issues ranging from intensive trawler fishing to oil pollution. By the mid-'70s, the Calypso was one of the most famous ships in the world. The country singer John Denver even wrote a song about the ship; Calypso, the song reached number 2 on the US Billboard charts.

The Calypso's career came to an ignominious end in January 1996 when it was hit by a barge in Singapore. Badly damaged, the venerable old ship sank, but fortunately, it rested only a few metres under the surface. Dragged out of the mud and brought back to France, the Calypso was left in limbo. Cousteau, always one to get the very best, was considering having an entirely new ship built, the Calypso II. Cousteau died in 1997, and with him went any hopes of the Calypso's resurrection. In 2007, still sitting in dry dock in Brittany, the quietly rusting and now mastless Calypso was given a lifeline. The French Maritime and River Heritage Foundation awarded the stricken vessel the status of Bateau d'Intérêt Patrimonial (Boat of Heritage Interest). Restoration work began but has, alas, been indefinitely interrupted by a myriad of technical setbacks and legal wranglings. The Calypso, it seems, must await another Loël Guinness if it is ever to recapture its former glory.