The Turtle was designed to dive to 6000 feet. When DSV-2 Alvin installed a new titanium hull, the Alvin steel hull was installed in the Turtle. The Turtle depth rating was then increased to 10,000 feet. It has a hull 2 inches thick,[citation needed] and a hatch about 3-1/2 inches thick held in place by the pressure of the water above it (it is tapered, narrower inward). The Alvin-class DSV's were designed to replace older DSV, such as the less maneuverable Trieste-class bathyscaphes.