Summary: The dynamic problems of a crack running perpendicularly into a half-plane surface and a cruciform crack running in an unbounded solid under the action of moving point forces are analyzed. The cracks are treated as dislocations distributed with respect to speed, so that the problems reduce to singular integral equations with Dirac functions as nonhomogeneous terms. By extracting physically significant limit cases with analytical solutions, the terms are removed, and the resulting equations solved numerically by a standard technique. Dynamic stress intensity factors and crack opening data are presented. For the cruciform crack, this data is compared with that for the plane crack limit case.