  The effect of quenched (frozen) orientational disorder on the collective
motion of active particles is analyzed. We find that, as with annealed disorder
(Langevin noise), active polar systems are far more robust against quenched
disorder than their equilibrium counterparts. In particular, long ranged order
(i.e., the existence of a non-zero average velocity $\langle {\bf v} \rangle$)
persists in the presence of quenched disorder even in spatial dimensions $d=3$,
while it is destroyed even by arbitrarily weak disorder in $d \le 4$ in
equilibrium systems. Furthermore, in $d=2$, quasi-long-ranged order (i.e.,
spatial velocity correlations that decay as a power law with distance) occurs
when quenched disorder is present, in contrast to the short-ranged order that
is all that can survive in equilibrium. These predictions are borne out by
simulations in both two and three dimensions.
