In 1958, they did a deal with the U.S. Navy, which gave the Navy ownership but left them in control. Now flush with funds, the Piccards rebuilt the vessel, giving it walls five inches thick and shrinking the windows to just two inches in diameter—little more than peepholes. But it was now strong enough to withstand truly enormous pressures, and in January 1960 Jacques Piccard and Lieutenant Don Walsh of the U.S. Navy sank slowly to the bottom of the ocean's deepest canyon, the Mariana Trench, some 250 miles off Guam in the western Pacific (and discovered, not incidentally, by Harry Hess with his fathometer). It took just under four hours to fall 35,820 feet, or almost seven miles. Although the pressure at that depth was nearly 17,000 pounds per square inch, they noticed with surprise that they disturbed a bottom-dwelling flatfish just as they touched down. They had no facilities for taking photographs, so there is no visual record of the event.
1958年，他们与美国海军达成一桩交易，把探海艇的所有权交给海军，但他们仍保留使用权。他们因此获得了大笔资金，对那条船进行了改造，把船壁的厚度加大到将近13厘米，舷窗缩小到只有直径5厘米——实际上成了小小的窥孔。但是，探海艇变得相当坚固，可以抵御巨大的压力。1960年1月，雅克·皮卡尔和美国海军的唐·沃尔什在西太平洋关岛外商大约400公里的地方，慢慢下沉到了海洋里最深的峡谷：马里亚纳海沟（这里要特别提一下，该海沟是哈里·赫斯用回声测探仅发现的）。他们花了不到4个小时就下沉到10918米，相当于差不多11公里。虽然在那个深度压力达到了每平方厘米将近1200千克，但他们吃惊地注意到，碰着底部时惊动了生活在海底的比目鱼。他们没有照相设备，因此没有记录下当时的情景。

After just twenty minutes at the world's deepest point, they returned to the surface. It was the only occasion on which human beings have gone so deep.
他们在世界的最深处只停留了20分钟，然后返回水面。人类只有这么一次达到了那种深度。
Forty years later, the question that naturally occurs is: Why has no one gone back since? To begin with, further dives were vigorously opposed by Vice Admiral Hyman G. Rickover, a man who had a lively temperament, forceful views, and, most pertinently, control of the departmental checkbook.
40多年以后，人们自然会提出这样的问题：为什么自那以来再也没有人下去？首先，再次潜水受到了海军中将海曼·G·里科弗的坚决反对。他这个人办事认真，说话算数，最关键的是他掌握着海军部的财政大权。