It is possible to generate a relatively uniform, highly ionized plasma by passing a powerful discharge between electrodes so arranged that the current is forced to flow across an initial strong magnetic field. The magnetic induction due to the discharge causes a bending of the original field. If the discharge is operated with a low-impedance current source, the electric breakdown starts in a limited region near the current-input connections (minimum-inductance path) and propagates as a well-defined front in the manner of a hydromagnetic shock wave. In this paper we analyze the phenomenon as a one-dimensional single-fluid hydromagnetic problem, neglecting dissipation behind the wave.