The Workhorse of the Deep

Over its 53-year history, the deep submersible Alvin has had some subtle and not-so-subtle changes made to its appearance. The original sub, shown in the late 1960s with support vessel Lulu, was stubby and had a white sail. Its stainless steel hull was replaced with a titanium personnel sphere in 1973, enabling dives to greater depths. In the 1980s, its sail was painted a distinctive red, making it easier to spot at the ocean surface, and its rear propeller was replaced with thrusters. Many more improvements were made over the years, and, in 2013, a major upgrade included installation of a new, larger, deeper-diving titanium sphere and new flotation, giving Alvin even better research capabilities and a sleeker look. (Photo by Cliff Hinton, Woods Hole Oceanographic Institution)