Vacuum Kerr-Schild metrics generated by nontwisting congruences

The Kerr-Schild pencil of metrics ${\tilde{g}}_{ab}=g_{ab}+V{l}_a{l}_b$, with $g_{ab}$ and ${\tilde{g}}_{ab}$ satisfying the vacuum Einstein equations, is investigated in the case when the null vector $l$ has vanishing twist. This class of Kerr-Schild metrics contains two solutions: the Kasner metric and a metric wich can be obtained from the Kasner metric by a complex coordinate transformation. Both are limiting cases of the K'ota-Perj'es metrics. The base space-time is a pp-wave.