If someone has figured out a way to control gravity/inertia with electromagnetic forces, this is what would be expected. Basically an "inertialess" drive. It also opens up space travel, even if only at sub light speeds.
Please. "Doc" Smith invented that in the 1930s. [/s]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Precisely. In General Relativity the force of inertia that operates in opposition to acceleration or deceleration is the combined gravity of the rest of the universe acting at each point. Shielding gravity from a particular direction would enable very rapid changes in velocity vector in the opposite direction without inducing the inertial forces that would crush metal, much less any living being. In fact, no other power source would be required as the "Drive" power comes from the pull of gravity in the non-shielded direction with little or no resistance.
The line of least resistance in "Free fall" is called the geodesic in spacetime. By changing the shape of the geodesic locally one creates the so-called "Wrinkle in Time" or "Tunnel in the Sky" of Heinlein. My tensor analysis is a little rusty, so I can't show how this can possibly result in faster than light travel, but my gut tells me it's related. After all, warping gravity locally entails a very large mass being close enough, in some sense, even though it is not that way (i.e., "Close") in our frame of reference.
Last point: Some theorists on the Internet suggest that the warping of the geodesic entails moving orthogonally to every direction in space, i.e., moving along the time axis of the 4D spacetime continuum...resulting in some apparently superluminal velocities.