  We present a hydrodynamic theory of polar active smectics, for systems both
with and without number conservation. For the latter, we find quasi long-ranged
smectic order in d=2 and long-ranged smectic order in d=3. In d=2 there is a
Kosterlitz-Thouless type phase transition from the smectic phase to the ordered
fluid phase driven by increasing the noise strength. For the number conserving
case, we find that giant number fluctuations are greatly suppressed by the
smectic order; that smectic order is long-ranged in d=3; and that nonlinear
effects become important in d=2.
