A parametric assessment of the D-D-fuelled fusion-fission hybrid reactor is undertaken. Based on the fusion hybrid reactor characteristic that the attainment of a "break-even" plasma is not essential for the maintenance of a viable system, its capabilities of net power generation and fissile fuel production at low plasma fusion gains are investigated in this paper. Analysis of the isotopic and energetic balances under steady-state conditions has resulted in the formulation of essential relationships involving fissile fuel yield, system power, fusion plasma efficiency, and plutonium content in the blanket material. The increasing systems design flexibility associated with the catalysed-D hybrid reactor suggests the definite possibility of an earlier introduction of advanced fusion cycles in the production of nuclear energy.