Abstract: There is disclosed an electrical generating plant, especially for use in a submarine, having dual modes of operation and which comprises a fuel cell which requires a supply of gaseous hydrogen and a supply of gaseous oxygen in order to generate an electrical output. First supply means supplies to the plant a hydrogen-containing compound, preferably methanol, which is liquid at NTP and which can undergo an endothermic reaction to liberate gaseous hydrogen, and second supply means is provided which is selectively operable for supplying to the plant liquid hydrogen peroxide in a first mode of operation and air in a second mode of operation. A reformer is connected to the first supply means and causes the hydrogen-containing compound to undergo the endothermic reaction with liberation of gaseous hydrogen, whereas a decomposer is selectively connectible to the second supply means, in the first mode of operation, and is arranged to decompose the hydrogen peroxide exothermically so as to liberate gaseous oxygen.