The Defence Evaluation and Research Agency are exploring the potential of electrothermal-chemical (ETC) gun technology. An important area is that of plasma ignition of solid propellant gun charges. An understanding of the energy transfer mechanisms from the metallic plasma to the propellant grain is central for optimisation of an ETC ignition system. This paper explores, both theoretically and experimentally, the energy transfer mechanisms involved in plasma-propellant interactions during plasma ignition of a conventional charge system, with a view to minimising the electrical energy requirements of an ETC gun system. A mechanism of energy transfer due to the condensation of metallic vapour onto the propellant grain is advanced and experimentation provides some evidence for this. In principle, it should be possible with vapour deposition to initiate self-sustaining combustion using very small quantities of electrical energy, provided the power transfer is greater than that required to accomplish self-sustained combustion processes. A 'vapour generator' may be required rather than a plasma generator for ETC ignition.