  We construct a hydrodynamic theory of active smectics A in two-dimensional
space, including the creation/annihilation and motility of dislocations with
Burgers' number $\pm1$. We derive analytical criteria on the set of parameters
that lead to flows. We show that the motility of dislocations can lead to flow
transitions with distinct features from the previously reported active
Helfrich--Hurault shear instability with, notably, a first-order transition in
the velocity from quiescence to turbulence.
