For centuries, the daredevils known as submariners have slipped beneath the waves in vehicles made for horizontal travel. Their craft are basically underwater ships. Even submersibles, small vessels that dive unusually deep, follow the horizontal plan.

Until now.

In a stroke, James Cameron has upended the field — literally and figuratively. A man known for imaginative films (“Titanic,” “Avatar”), he has reinvented the way that people explore the deep ocean.

This month, Mr. Cameron unveiled his unique submersible and announced plans to ride it solo into the planet’s deepest recess, the Challenger Deep in the western Pacific, nearly seven miles down.

He calls it a vertical torpedo. The axis of his 24-foot-long craft is upright rather than horizontal, speeding the plunge. His goal is to fall and rise as quickly as possible so he can maximize his time investigating the dark seabed. He wants to prowl the bottom for six hours.