One of the biggest difficulties is pressure. An increase of 10 meters in depth will increase atmospheric pressure. A cup of plastic foam will be reduced several times in a few thousand meters deep water. Deep sea diving can only be carried out by high pressure submersible, and it can't get out of the cabin like astronauts.
In 1930, American marine biologist Bibby and engineer Barton dived 183 meters with a diving ball. In 1934, they set a record of 914 meters, which became the news of the world at that time. Hollywood also invited the handsome young Barton to make a film. However, the steel diving ball depends on the sling up and down, and the weight is too large. It is unrealistic to dive for thousands of meters. We need innovative ideas at the source. In 1953, Swiss Professor Picard proposed to transplant the principle of balloon to deep diving technology, and add a floating body filled with gasoline in addition to the steel ball. Instead of relying on slings, it depends on buoyancy up and down, realizing a technological breakthrough. In 1960, Professor Picard's son, engineer J. Picard and US Navy officer Walsh drove the "QUST" submersible to the bottom of the Pacific Mariana Trench at a depth of 10916 meters, setting a world record that has not been broken so far.
Today, in the 21st century, deep diving technology has developed vigorously. There are not only much more advanced manned deep submersibles, but also unmanned deep submersibles - underwater robots. 2012 is a memorable year in the history of deep diving: in July, China's manned deep submersible Jiaolong dived to the 7062 meter deep sea bottom of the Pacific Ocean, marking China's ability and determination to explore the deep sea.
The Chinese Jiaolong manned submersible is similar to the American Alvin. It can take three people to dive, but the passengers can't be too fat. The combined weight of the three people can't exceed 240 kg. Jiaolong is much better than Alvin in terms of its technical performance and diving depth. However, Alvin is much richer than Jiaolong in terms of application and diving experience. The Jiaolong is 8.2 meters long, 4.1 meters wide, 3.4 meters high and weighs 22 tons. It can go down to more than 7000 meters underwater; The submersible has seven propellers and can move independently. The sampling basket outside can carry equipment or samples weighing 220 kg. After experiments, Jiaolong dived to 5038 meters in the South China Sea in 2011 and 7062 meters in the Western Pacific in 2012. In 2013, it began to carry out the first experimental application voyage in the South China Sea and the North Pacific to carry out scientific research on marine biodiversity.