A lumped-parameter (slug) model of the explosively driven MHD pulse generator is treated. The modes of operation of the device are cataloged. An analytical expression is derived for the dependence of the conversion efficiency of the device on its parameters: the magnetic Reynolds number, the load-to-channel inductance ratio, and the ratio of initial magnetic and kinetic energies. Some aspects of this dependence are studied in detail. It is shown that the load inductance establishes an upper bound on the energy gain (energy delivered/initial magnetic energy), and also determines the degree to which the magnetic excitation can be reduced without serious sacrifice of efficiency. Performance measures for the device are denned. The role played by the ratio of the load and slug resistances in the optimization of the performance is discussed.