A hard X-ray spectrometer (HXRS) was developed jointly by the National Oceanic and Atmospheric Administration (NOAA) Space Environment Center and the Astronomical Institute of the Czech Republic to determine if proton storms could be forecast with greater accuracies than presently available by the existing methods. The HXRS experiment was conceived as a means of proof testing previously discovered empirical relationships between anomalous hard X-ray spectra of hard X-ray flares and solar energetic proton events (SEPs) for space weather forecasting applications. SEPs are showers of highly energetic electrons and ions, mostly protons, that can reach Earth's vicinity within minutes to hours following a moderate to large flare and have the potential of affecting the performance of civilian, military and research satellites as well as certain surface assets. The primary SEP predictor criterion educed during the present study is the requirement that the spectral index, γ, must decline (harden) to at least ≤4 for at least 3 min. Flares meeting this criterion have a high association with SEPs. Flares that fail this criterion do not. Other SEP correlative phenomena such as depressed hard X-ray flux and anomalous low temperatures were studied to determine their utility for forecasting purposes. During the study period, March 2000 through December 2002, 107 hard X-ray flares were spectrally analyzed including 16 SEP-associated flares. Fourteen SEP flares were correctly identified, two SEPs were missed, and three false alarms (untrue predictions) were incurred.