<P> The Navy commissioned Ballard and his team to carry out a month - long expedition every year for four years, to keep Argo / Jason in good working condition . It agreed to Ballard's proposal to use some of the time to search for Titanic once the Navy's objectives had been met; the search would provide an ideal opportunity to test Argo / Jason . In 1984 the Navy sent Ballard and Argo to map the wrecks of the sunken nuclear submarines USS Thresher and USS Scorpion, lost in the North Atlantic at depths of up to 9,800 feet (3,000 m). The expedition found the submarines and made an important discovery . As Thresher and Scorpion sank, debris spilled out from them across a wide area of the seabed and was sorted by the currents, so that light debris drifted furthest away from the site of the sinking . This "debris field" was far larger than the wrecks themselves . By following the comet - like trail of debris, the main pieces of wreckage could be found . </P> <P> A second expedition to map the wreck of Scorpion was mounted in 1985 . Only twelve days of search time would be left at the end of the expedition to look for Titanic . As Harris / Grimm's unsuccessful efforts had taken more than forty days, Ballard decided that extra help would be needed . He approached the French national oceanographic agency, IFREMER, with which Woods Hole had previously collaborated . The agency had recently developed a high - resolution side - scan sonar called SAR and agreed to send a research vessel, Le Suroît, to survey the sea bed in the area where Titanic was believed to lie . The idea was for the French to use the sonar to find likely targets, and then for the Americans to use Argo to check out the targets and hopefully confirm whether they were in fact the wreck . The French team spent five weeks, from 5 July to 12 August 1985, "mowing the lawn"--sailing back and forth across the 150 - square - mile (390 km) target area to scan the sea bed in a series of stripes . However, they found nothing, though it turned out that they had passed within a few hundred yards of Titanic in their first run . </P> <P> Ballard realized that looking for the wreck itself using sonar was unlikely to be successful and adopted a different tactic, drawing on the experience of the surveys of Thresher and Scorpion; he would look for the debris field instead, using Argo's cameras rather than sonar . Whereas sonar could not distinguish man - made debris on the sea bed from natural objects, cameras could . The debris field would also be a far bigger target, stretching a mile (1.6 km) or longer, whereas Titanic itself was only 90 feet (27 m) wide . The search required round - the - clock towing of Argo back and forth above the sea bed, with shifts of watchers aboard the research vessel Knorr looking at the camera pictures for any sign of debris . After a week of fruitless searching, at 12.48 am on Sunday 1 September 1985 pieces of debris began to appear on Knorr's screens . One of them was identified as a boiler, identical to those shown in pictures from 1911 . The following day, the main part of the wreck was found and Argo sent back the first pictures of Titanic since her sinking 73 years before . The discovery made headlines around the world . </P> <P> Following his discovery of the wreck site, Ballard returned to Titanic in July 1986 aboard the research vessel RV Atlantis II . Now the deep - diving submersible DSV Alvin could take people back to Titanic for the first time since her sinking, and the remotely operated vehicle (ROV) Jason Jr. would allow the explorers to investigate the interior of the wreck . Another system, ANGUS, was used to carry out photo surveys of the debris field . Jason Jr. descended the ruined Grand Staircase as far as B Deck, and photographed remarkably well preserved interiors, including some chandeliers still hanging from the ceilings . </P>

Who discovered the titanic wreck site and when
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