  Looking at current proposals of so-called `warp drive spacetimes', they
appear to employ General Relativity only at an elementary level. A number of
strong restrictions are imposed such as flow-orthogonality of the spacetime
foliation, vanishing spatial Ricci tensor, dimensionally reduced and
coordinate-dependent velocity fields, to mention the main restrictions. We here
provide a brief summary of our proposal of a general and covariant description
of spatial motions within General Relativity, then discuss the restrictions
that are employed in the majority of the current literature. That current warp
drive models are discussed to be unphysical may not be surprising; they lack
important ingredients such as covariantly non-vanishing spatial velocity,
acceleration, vorticity, together with curved space, and a warp mechanism.
