Quickly they climbed into the sphere and sealed the hatch behind them. Only a single bolt was used to hermetically seal them in, the thousands of pounds of pressure outside would ensure it stayed shut. At 0823 hours they began their dive and the Trieste became calm for the first time in days as it slipped below the waves. Though the nerve wracking task of descending to depths never seen before lay in front of them, they were somewhat happy to be in this position so they did not have to experience the waves and storms that the remaining crew would. The bathyscaphe slowly descended, only reaching 300 feet in 10 minutes but this was by design so the men could do any final checks that were needed.

Unfortunately an issue had already risen, they had reached the level where water cooled rapidly and completely halted their descent. In cooler water the relative weight of the craft was diminished so it would no longer sink. There were only two options, wait for the gasoline to cool to the outside water temperature or release some gasoline to bring down their weight. Both options held risks. Waiting meant that they might disrupt their timeline and it was imperative that they returned to the surface while it was still daylight. However if they released some of the gasoline then they might not have enough left to make their return to the surface. After a minute of deliberation the men decided to release some of the liquid. They were confident that their fuel calculations were correct and would not need the extra 150 cubic feet of extra gas they had brought along. After releasing their reserve they would have 4,000 cubic feet of gasoline left to lift them to the surface. Piccard opened the gas valve to allow some of the fuel to escape and after about a minute they began to descend once again. The valve was closed to keep what they could of the reserve tank but after descending only 35 more feet they hit another layer of cooler water and were halted again. More gas was released to resume the dive. Five minutes after this second halt, at a depth of 425 feet, they were stopped once more by another layer and had to release even more fuel. Seven minutes later they were stopped again at a depth of 530 feet and had to release more of the precious liquid. Jacques later stated that “This was the first time in my 65 dives in the Trieste that I had observed this phenomenon of repeated stratification.”

There was an upside to all of these stops however, they were able to watch their new electric thermometer and accurately take temperatures of the thermocline. This information would be helpful to oceanographers in defining the different temperature zones of the ocean.

After diving 650 feet the problems appeared to be over as the men were now descending at a steady rate of four inches per second. The true dive was just now beginning as they had nearly seven miles to go. Luckily as the men continued to dive deeper and deeper the increased pressure would add weight and cause them to descend faster, eventually coming to a mean speed of three feet per second. The only time Piccard or Walsh would interfere with the process was when they released ballasts to ensure they were traveling at a safe speed.