The dynamic response of a planar target irradiated by a tightly pinched intense relativistic electron beam is found to be very sensitive to in‐depth heating by the beam due to x‐ray deposition and to diode voltage fluctuations. We find that voltage fluctuations are primarily responsible for the observed wave structure preceding the large‐amplitude shock wave while x‐ray deposition affects the response to a lesser extent. The implications of these results for electron‐beam fusion target and accelerator designs are noted.