The day China and other parts of the world were waiting for finally came!

On June 24 2012, the Jiaolong manned submersible started its journey toward a depth of 7,000 metres at 141°58.50' E and 10°59.50, N in the Mariana Trench of the north-west Pacific Ocean. At 6:30 a.m. it was raining heavily, and the waves whipped spray high up into the air. A sail-off ceremony was held for the oceanauts on the deck of the Xiangyanghong 09 mothership by the on-scene headquarters and the Provisional CPC Committee.

The night was lit up by the lights on deck, which also illuminated the banner that read, "The sail-off ceremony for the oceanauts of the 7,000-metre sea trial." Since its approval in 2002, the Jiaolong project had conducted four trials up to 2012. Therefore, the target of 7,000 metres was quite familiar. Today, the goal was finally turned into a reality, after so many challenges.

All the members of headquarters and the Provisional CPC Committee, in blue uniforms and security helmets, stood in rows and stared at the words on the banner. Enthusiasm filled their hearts. Great responsibility fell on the three oceanauts, namely Ye Cong, the engineer and chief oceanaut, Liu Kaizhou, research associate of CAS Shenyang Institute of Automation, and Yang Bo, research associate from the CAS Institute of Acoustics. They stood at the front of the squad with an easily recognizable Five-star Red Flag on the left breast of their uniforms, their faces glowing with vitality.

The ceremony was chaired by Secretary Liu Xincheng.

Chief Commander Liu Feng looked serious and determined. Following some brief remarks to the oceanauts heading toward 7,000 metres for the first time, he announced that, "The trial starts now!"

Members of the on-scene headquarters and the Provisional CPC Committee shook hands with, or opened arms to, the three warriors. Pats on the back, rather than words, delivered the message. It was a message of deep trust as well as sincere good wishes.

The three oceanauts walked one after another into the vehicle from the maintenance platform. The chief pilot, Ye Cong, was the last to enter. He turned to the crowd and waved his hand as a sign of his confidence and determination. Despite the heavy rainfall, nobody left the scene. Instead, every department carried on working as planned. Clothes were drenched, but hearts were full of sunshine.

At 7 a.m., the headquarters called on everyone to get ready. Moving the railcar, removing the bolt, hanging the main cable, lifting and setting up the A-frame, attaching the cable to the head of the submersible and then placing it in water and removing the cables, were tasks completed all in one breath. Slowly, the submersible started to drift from the stern of the mothership. Not far away, Haiyang 6 was on guard duties.

Since the public media coverage of Jiaolong's 5,000-metre sea trial, the sea trial team had set up a system for press conferences in which Party Secretary Liu Xincheng was the spokesperson on the scene, to ensure a consistent message was delivered. At this point, he made the official announcement to the press on board: "Jiaolong dived into the water at 7:29 and set up digital communication at 7:33. Now it is diving at 41 m/s. Facilities on the submersible are working and the oceanauts are in good condition."

Data on the screen at headquarters kept updating: 1,000, 2,000, 6,000....  The deeper the submersible went, the more pressure Liu Xincheng was feeling. It was never a problem that Jiaolong ran into Typhoon Mawar and Guchol. Variable ballasts and propellers were thwarted by the high pressure in the deep sea, but the team rose to the challenge despite the difficulties. Frustration, tears and failure existed from time to time, but the journey was always accompanied by flowers, letters of congratulation and applause. More memories came upon him. But he shut the door of the past due to limited time. At 10:05, Chief Commander Liu Feng reminded him that it was time for the second announcement."

Having checked the data and cleared his throat, Liu Xincheng spoke to the reporters. "Jiaolong reached 6,000 metres at 10:04 and is now diving at 35 m/min." Ye Cong reported that the systems were working and the oceanauts were in good condition.

Headquarters was so silent that it was possible to hear a pin drop. People fixed their eyes on the screen and rubbed them to see the flickering figures more clearly: 6,900 metres, 6,935 metres, 6,970 metres... At 10:55, 7,005 metres popped up on the screen, triggering loud cheers and lengthy applause. This was a new depth record for the whole world. Liu Feng and Liu Xincheng could not help but stand up with hands clutched tightly.

The Chief Commander's eyes were wet once again. The Secretary of the Provisional CPC Committee contained his excitement as he was live on CCTV to update the public on the performance of the Jiaolong sea trial team. On the same day, Shenzhou 9 cruising in outer space, was scheduled to manually dock with Tiangong 1, the space station launched earlier. If it succeeded, then the day would be marked with two miracles, one in the sky and one in the ocean!

The thrilling moment came as we spoke.

At 11:25 local time, or 9:07 Beijing time, on June 14 2012, the report from the chief pilot, Ye Cong, arrived. "Xiang 9! Xiang 9! Jiaolong, at 9:07 Beijing time, 24th June 2012 reached the bottom at 7,020 metres. Oceanauts Ye Cong, Liu Kaizhou and Yang Bo wish the Tiangong 1 docking, by Jing Haipeng, Liu Wang and Liu Yang, every success! We wish China's manned space travel and manned deep diving programmes great success!"

Liu Xincheng's voice trembled. "As all of you have heard that, I will not announce it again. Our Jiaolong has just made history!"

None of the journalists present from Xinhua News Agency, CCTV, Science and Technology Daily and China Ocean News raised his head. They simply nodded and kept their hands busy tapping on the keyboards on their laptops, releasing the big news as soon as possible.

Another amazing story was reported later in that night's broadcast by Xinwen Lianbo of CCTV. When Jiaolong's 7,000-metre dive was confirmed, together with the successful manual rendezvous and docking between Shenzhou 9 and Tiangong-1, the astronauts were shown sending greetings to the oceanauts. The astronauts Jing Haipeng, Liu Wang and Liu Yang could be seen floating in the orbiting cabin of Tiangong-1 in their blue uniforms, with the same symbol of the bright red national flag on their chests. Commander-in-Chief Jing Haipeng spoke on behalf of the three astronauts.

"We, the three astronauts, would like to extend congratulations to oceanauts Ye Cong, Liu Kaizhou and Yang Bo, who have dived 7,020 metres into the Pacific Ocean. This is a remarkable achievement for China's manned deep-sea exploration programme!"

China's two major new science and technology breakthroughs were circulated to the world via electromagnetic waves. This was a historic moment! The Chinese oceanauts, 7,020 metres below the surface of the sea, and the astronauts, far away in space, were sending greetings and encouragement to each other, each recognizing the great worldwide significance and influence of the other. Both these science and technology achievements had greatly inspired and motivated the Chinese people, enhanced the national image and status.

After Jiaolong's first 7,000-metre dive into the Mariana Trench, the sea trial crew made a second 7,000-metre sea trial dive on 19th June, led by Tang Jialing, Yu Hang and Zhang Dongsheng's team. They descended to a maximum depth of 6,965.25 metres and completed many tasks including near-bottom cruising, balancing, fixed-depth voyaging, lighting adjustments, photography, microtopology measurements, sitting three times on the bottom, collecting water samples and sediments and placing marker. The marker said "The 47th Dive of China's Manned Deep-Sea Submersible Jiaolong". The spot where the submersible sat on the bottom was exactly the same as in the plan, demonstrating the excellent performance of Jiaolong's underwater navigation and positioning systems.

However, this dive was followed by some external confusion and doubt. Why didn't Jiaolong reach the depth of 7,000 metres when it had already descended over 6,960 metres, leaving only a few more metres to go? Was it because something had gone wrong with the submersible, or was the sea floor not suitable for diving further? Opinions differed, and no agreement was reached. Many people thought that Jiaolong had missed a good chance to achieve the target all in one step, which seemed to be a pity.

In fact, the second dive was based on the "Jiaolong Manned Submersible 7,000-metre Sea Trial Implementation Proposal" approved by the SOA and the MOST, which was a solid and deliberate plan. However, the on-site headquarters decided to hold a media briefing to provide an explanation and clear up the doubts in people's minds.

The meeting was held in the meeting room of the ship Xiang 9 and chaired by Secretary Liu Xincheng. Chief Commander Liu Feng first presented the third dive plan and then explained why the second dive didn't descend directly to 7,000 metres. "There are three major reasons. Firstly, the sea trial leading group approved a plan for 'four plus two dives', i.e., four valid dives and two back-up dives, which would be performed from 5,000 metres to 6,000 metres and then on to 7,000 metres accordingly. None of the first three dives was to descend further than 7,000 metres. We are carrying out the complete plan. Secondly, over 200 testing and validation programmes must be performed at 6,000 metres. The variable ballast system and the altimeter malfunctioned in the second dive and failed to pass the test. Thirdly, we must coordinate with Beijing before the 7,000-metre dive is made, and carry out the plan step by step, as the higher authorities may have some input to the arrangements. We plan to launch the fourth dive on 25th June, aiming at 7,000 metres, all being well..."

Liu Xincheng added, "The second dive to 6,965 metres in particular has triggered heated discussion and has even found critics in many fields in our country. All the discussions focused on three aspects: first, feeling disappointed that we didn't reach 7,000 metres, second, asking why we didn't reach 7,000 metres and third, thinking that there may be something wrong with the testing. These discussions showed that the public was seriously concerned about the test and about China's manned deep-sea programme, which meant that our work had not been fully publicized. Prudence and truth-seeking is vital to the spirit of China's manned deep-sea programme. What the sea trials aim for is more than simply depth. They also value gradual and practical step-by-step processes, developing the capability to find problems and address them in time so that deep-sea technologies can be better applied in our marine endeavours. In order to solve the problem with the control circuit board for the seawater pump in the variable ballast system, the electrical and power distribution team worked until 3 o'clock in the morning, demonstrating their devotion and the value of their contribution. The team would not allow lurking problems to remain unresolved after the test completion. It was this kind of scientific attitude that we had kept in mind all these years. Tomorrow's test would repeat the second dive's experiments and confirm the validation of the variable ballast system and altimeter after troubleshooting at a depth of less than 7,000 metres. We hoped our media friends could explain the prudent and truth-seeking spirit and scientific attitude of the sea trial crew to the general public."

On the next day, 22nd June, a team led by Fu Wentao, Yu Hang and Ye Cong performed the third 7,000-metre dive. The maximum depth was 6,963 metres, and more brilliant achievements were made. Seabed operation lasted over three hours, during which time the submersible sat on the bottom six times, collected three sediment samples, three water samples, two black concretion blocks and one creature (a transparent sea cucumber). It also took photos of seabed creatures. It completed the function review of the injection system and the charging of the variable ballast and propellant and deployed imaging sonar, doppler velocimetry, crash avoidance sonar, lighting and cameras, while observing work conditions, etc. These fruitful results further demonstrated the outstanding performance of Jiaolong in the deep sea.

Before the testing team returned to the deck, Fu Wentao made a call to a marine environment scientist from the Second Institute of Oceanography, via very high frequency telecommunications, asking him to prepare a plate. People at the on-site headquarters immediately became excited, thinking that a deep-sea creature had been captured! They all ran automatically towards the aft deck. After the railcar returned to its position, people rushed towards the sample collection basket one after another, and even the journalists were squeezed to the outside of the circle. Liu Chenggang took out a sample plate and carefully put on rubber gloves. Helped by many people, he stepped onto the railcar and with one foot in the air carefully picked up a transparent sea cucumber from the biological sample collection basket. Other people rapidly lifted up the sample plate. Liu Chenggang put the sea cucumber on the plate and said, "We need seawater."

"Here's the seawater," everyone echoed. Two barrels of seawater prepared as gifts for the oceanauts had already been placed at the door of the submersible vehicle preparation room.

When the big wooden plate was placed on the hatch, it was immediately surrounded by people wondering what the sea cucumber from the Pacific Ocean sea floor would look like. Liu Chengang took out a board measure he had previously prepared, to measure the transparent sea cucumber, which was 15 centimetres long. Professor Yu who had been on the dive trip said, "It has shrunk. It was quite big on the sea floor. If it had been as small as this, the mechanical arm would never have been able to catch it."

"Headquarters knew you had found a lot of sea cucumbers, shrimps and other creatures, but didn't realize you had collected such a valuable biological sample," said Liu Feng.

"Haha, I asked them not to mention it because I wanted to give you a surprise. We found this sea cucumber underwater and set out to catch it. Fu Wentao operated the mechanical arm with Ye Cong's guidance and we finally got it. We were afraid it would escape, so Fu Wentao kept pressing on the lid of the biological collection basket with the mechanical arm..."

They had also found two metallic nodules on the sea bed which had irregular shapes and looked like halobolite. The nature of the substance was still to be researched. According to general knowledge, metallic nodules can only be found in ocean basins. However, these were discovered in the Mariana Trench, which was a world first and therefore had tremendous academic value. Though this deep-sea dive didn't exceed a depth of 7,000 metres, it tested all the submersible vehicle functions and collected precious biological and mineral samples, making it a very fruitful dive.

Meanwhile, Liu Cigui, the Director of the SOA, spoke with the on-scene headquarters via a video link. He said, "Today's dive has gone very smoothly. Congratulations again. I want to discuss one issue with you. The dive to a depth of 7,000 metres is supposed to take place on Monday 25th June, a workday. If the dive takes place on Sunday 24th, it will attract greater publicity. However, it depends on the on-site situation. Don't push yourselves if you are short of time for preparation. Safety is still the primary consideration."

Liu Feng looked at Liu Chengxin beside him and answered, "OK, Director Liu, we will do some research and try to make it one day earlier."

Thus, it was the leadership of the SOA who proposed breaking through the 7,000-metre barrier on 24th June. However, they did not expect that they would have the means to communicate with outer space. The sea trial team, far away from the homeland, couldn't watch television news and had no mobile phone network signal. The team received the news of the successful launch of the Shenzhou 9 manned spacecraft on 16th June only though the domestic news digest sent by the North China Sea branch of the SOA. They knew nothing about any other news. Furthermore, because of the tight deadlines of the sea trial tasks, the team members worked seven days a week. They were not conscious of the date and paid no attention to other matters.

At the headquarters conference that night, Liu Feng conveyed the spirit of Director Liu Cigui's words and asked whether the dive to a depth of 7,000 metres could take place one day earlier if the situation allowed.

Cui Weicheng, the Deputy Commander in charge of the submersible vehicle, spoke first. "I think it is feasible. Although the variable ballast is currently experiencing some problems, this has no effect on any of the test items except for the rising speed."

Professor Yu, the leader of the expert advisory group, added that "from a technical perspective, the variable ballast failure would not influence other tests. Currently, Jiaolong's equipment is performing well. I agree that the 7,000-metre dive should take place on the 24th, considering the overall situation."

Other attendees also agreed. Liu Feng concluded, "OK. We will prepare for the 7,000-metre dive with a deadline of the 24th!''

After the conference, the headquarters reported the new proposal to Beijing and informed the crew immediately once approval was gained. At 10 o'clock that very night, Luo Sha, a Xinhua News Agency reporter who was aboard in order to conduct interviews, went to Liu Xincheng's room and said pleasantly and mysteriously, "Secretary Liu, there is news from our agency that the Shenzhou 9 docking with Tiangong will take place on 24th June, the same day we make the 7,000-metre dive."

Liu Xincheng's eyes lit up. "What a coincidence!" he thought.

Luo Sha added, "I think we can have the deep-sea oceanauts speak to the astronauts in outer space. That would be a particularly meaningful scene."

"Sure, let's talk to the commander about it." They went to Liu Feng's room immediately.

Liu Feng agreed. "This is a good idea. But first, the issue of direct acoustic communication should be resolved. Luo, call Zhu Min and discuss it immediately."

Zhu Min, the director of Jiaolong's acoustic system and an expert on acoustics, thought for a while after hearing the idea and then said, "The oceanauts communicate with the mother ship through water, while people on earth communicate with the astronauts via radio. The two media are different, making direct communication difficult. But we can transfer it through the aerospace control Centre."

Young Luo immediately said that Xinhua News Agency and CCTV could undertake the transfer job. The tasks were identified and delegated. Then, they all began work on their set tasks.

On 24th June, Ye Cong dived and sent blessings from the three oceanauts to the three astronauts. When he reached a depth of 7,020 metres, Ye transmitted photos and audio messages to on-site headquarters on the ship Xiang 9. The CCTV team created a direct video connection to the CCTV station for the transmission. Then, the photos and audio messages were transmitted to the Beijing Aerospace Control Center and on to the Shenzhou 9 spaceship in outer space by the centre.

Soon, the blessings from the astronauts in outer space were passed on to the deep-sea oceanauts in the same way. Both sides were deeply inspired. The videos were immediately broadcast to people all over the country and the world and became a great inspiration to all. It had a sensational effect and was a great historical event.

The Chinese are approaching the vastness of outer space and the depths of the sea!

At that moment, Director Liu Cigui at the sea trial support centre in Beijing spoke via video connection with Jiaolong's test dive oceanauts sitting on the bottom of the Mariana Trench at a depth of 7,020 metres.

Liu spoke pleasantly and excitedly. "Hello, Ye Cong, Liu Kaizhou, Yang Bo! Firstly, I'd like to extend warm congratulations upon your success in the 7,020-metre dive, on behalf of the State Oceanic Administration of China and the sea trial leading group! We have paid close attention to the whole diving process and feel excited and proud of you. People all over the country are also following your success through media coverage. I hope that you can continue your efforts and achieve even greater things in the next step of the trial, ensuring the success of the sea trials!"

Ye Cong spoke on behalf of the three oceanauts. "It is really good to hear Director Liu's words clearly at the sea bottom, at a depth of 7,020 metres. While sitting on the bottom, we have completed several tasks, including placing a marker, sampling the water and taking photos and videos. The three oceanauts are in good condition. We are proud of Jiaolong. Thank all the leaders and friends who are concerned with and support diving!"

This speech was also transferred: the audio and video from Beijing was transmitted to headquarters on Xiang 9 via satellite. Researcher Zhu Min placed a microphone in front of the speaker, transformed the audio signals into water signals and sent them to Jiaolong. The signals then were converted back into audio signals. The quality of the converted audio was very good.

Jiaolong sat at the bottom of the ocean twice and obtained two non-pressure-maintained samples and one pressure-maintained sample. It also placed several markers. In the process of rising back to the surface, the variable ballast system was reviewed. It was found that the water injection and drainage systems both functioned well. The scheduled assignments were soon finished. Jiaolong surfaced at 17:26 and rejoined the mothership at 18:12. When the test dive oceanauts exited from the hatch, they displayed the national flag which had been taken down to the Mariana Trench, a scene which was photographed by a number of well-equipped reporters.

The banner on the duty deck was changed to "Ceremony for the Oceanauts' Success in Chinese Manned Submersible Dive to a Depth of 7,000 Metres". With Secretary Liu Xincheng as host, Ye Cong reported to the Chief Commander on behalf of Liu Kaizhou and Yang Bo. "I'd like to report to you that we three oceanauts have finished the test tasks of the 49th dive and have succeeded in diving to a depth of 7,020 metres, returning safely and smoothly!"

Liu Feng said, "Your hard work is appreciated. Welcome and thank you!"

Liu Xincheng said, "Please offer flowers to the heroic test dive oceanauts!"

Chen Yu, a female reporter from Science and Technology Daily, presented gaily-coloured silk flowers to the three oceanauts and hugged each of them amid loud applause. Chen Chongming, the Political Commissar of Xiang 9, handed champagne to the oceanauts. They extracted the cork and gave the bottle a good shake. The bubbles burst out into the sky and the ocean.

The three oceanauts, representing and symbolizing the whole Jiaolong team, had achieved a remarkable performance and fulfilled the mission.

(selected from Jiaolong's Sea Explorations by Xu Chen, published by China Intercontinental Press in 2019)