Answer: Bathyspheres

For centuries, the best that scientists could do to study and catalog deep sea creatures was to wait, hopefully, for some of them to wash up on shorelines or be dredged up in fishing nets. As you can imagine, the depths of the sea and the numerous and diverse creatures found therein were so mysterious and removed from early marine biologists as to be almost mythical in nature, for none had ever been observed in their natural habitat. Despite the various diving suits, bells, and other diving machines created in the 18th and 19th centuries by curious scientists and inventors, none were structurally sound enough or advanced enough to actually descend to any notable depth.

That all changed in 1930 when the naturalist William Beebe and the engineer Otis Barton descended deep into the ocean off the coast of Bermuda in the Bathysphere—a spherical deep-sea submersible of Barton’s creation. The Bathysphere was most notable for its windows and structural integrity. Submersible vessels of the day were both limited in the depth they could attain (their designs limited them to dives of 383 feet or less) and, more importantly, they were windowless—making them useless for any sort of observation of sea life.

In the Bathysphere, not only did the pair set multiple deep sea diving records with their consecutive and increasingly bolder descents (the deepest of which put them 3,028 feet below sea level during the latter part of 1934), but it was the first time a scientist was afforded the opportunity to observe deep-sea animals in their natural habitat thanks to the vessel’s windows.