  The diffraction of a time-harmonic plane wave on collinear finite defects in
a square lattice is studied. This problem is reduced to a matrix Wiener-Hopf
equation. This work adapts the recently developed iterative Wiener-Hopf method
to this situation. The method was motivated by wave scattering in continuous
media but it is shown here that it can also be employed in a discrete lattice
setting. The numerical results are validated against a different method using
discrete Green's functions. Unlike the latter approach, the complexity of the
present algorithm is shown to be virtually independent of the length of the
cracks.
