In the South Korean Navy the demand for many spare parts is infrequent and the volume of items
required is irregular. This pattern, known as non-normal demand, makes forecasting difficult. This
paper presents a case study using data obtained from the South Korean Navy to compare the
performance of various forecasting methods that use hierarchical and direct forecasting strategies for
predicting the demand for spare parts. A simple combination of exponential smoothing models was
found to minimise forecasting errors. A simulation experiment verified that this approach also
minimised inventory costs.