  Impulsive gravitational plane waves, which have a delta-function singularity
on a hypersurface, can be obtained by squeezing smooth plane gravitational
waves with Gaussian profile. They exhibit (as do their smooth counterparts) the
Velocity Memory Effect: after the wave has passed, particles initially at rest
move apart with non vanishing constant transverse velocity. A new effect is
that, unlike to the smooth case, (i) the velocities of particles originally at
rest jump, (ii) the spacetime trajectories become discontinuous along the
(lightlike) propagation direction of the wave.
