The domain wall dynamics in `easy axis' anisotropy films without magnetic loss is considered. Similar to the Walker model of the infinite one-dimensional domain wall, the dipole-dipole interaction is responsible for the presence of a critical velocity in this case. However, its experimentally measured value is small compared to Walker's velocity for bulk materials. This fact is connected with the effective demagnetization factor reduction when decreasing d - the film thickness. Comparison with the experimental results obtained for ultrathin cobalt films with `easy axis' anisotropy shows excellent agreement of theory and experiment. The influence of the relatively weak planar (perpendicular to the anisotropy axis) magnetic field on the dynamics of the domain wall and its critical velocity is also analyzed.