Dynamic fracture parameters have been determined for two heat treatments of HF-1 steel. A gas gun was used for the experiments. Different amounts of fracture damage were produced in HF-1 steel specimens under known impact conditions. The specimens were soft recovered, sectioned, and polished to reveal any internal microscopic fracture. The fracture cracks were then digitized. The velocities of the 1.15-, 1.59-, and 2.37-mm-thick impactor disks range from 0.120 to 0.276 km/s. The specimen disks were 3.18- and 6.35-mm thick. An SRI stress wave propagation computer program with a brittle fracture model was used for calculating the dynamic fracture parameters. A series of Hugoniot experiments was performed for HF-1 steel to determine equation of state input data for the computer program. The Hugoniot elastic limits were 2.2 and 2.4 GPa for the two heat treatments.