At 8.2 meters long and 3.4 meters high, Jiaolong weighs around 22 tons.

Before each sea trial, Jiaolong had to be lifted from its mother ship and put into the sea, he says.

"When we were releasing Jiaolong for the first time (in the sea), it was blown away by the wind, and the mother ship had to find the exact angle for the frogmen to tie it back to the vessel," Yang says. "It was also the first time we got data from the sea.

"But the communication system was not working, as the signal from Jiaolong was swallowed by the noise of the sea. It was like trying to talk in a busy market with someone, without being able to hear each other."

Yang and other team members took two-hour naps each night for two weeks on the mother ship to solve the problem and the communication finally worked in a 50-meter trial.

Then came the 300-meter trial which took around 20 times to achieve.

"We had collected nearly 300 sets of monitoring data, but we could call the depth as passed only after all data were measured twice," he adds.

Yang remembers that at 300 meters below sea level it started to get dark, but the creatures were attractive.

"I saw many kinds of corals and different fish that I had never seen before," says Yang, who had never been to sea until this trial in 2009 and all he knew about sea creatures were from books or documentaries.

The team tried 1,000 meters before heading back to the laboratory to upgrade the vessel.

In the first half of 2010, Jiaolong was back in the South China Sea for a second round of trials-this time the goal was 3,000 meters. Yang recalls that problems occurred while diving below 2,200 meters, but they vanished when floating up. "If we met certain problems, the trial must be stopped and we had to immediately float up to solve them."

The trials for 3,000 meters went well for the last few times. The submersible went down into the sea 35 meters per minute, and each trial took around 10 hours. On each trial day, Yang and two other pilots set off in the vessel in the morning and returned before sunset. Yang also had some seasickness.

"The floating up time was the most relaxing time for us, pilots, as we can observe the sea, chat and eat."