The “caterpillar drive” in The Hunt for Red October allowed the sub to travel virtually undetected through the ocean, but real examples of magnetohydrodynamic drives (MHDs) are rare.

Now, 30 years after the movie, Darpa is working on a marine propulsion system similar to the "caterpillar drive" described in the movie. Called a magnetohydrodynamic (MHD) drive, the system has no ...