Manganin gauges have been embedded in AD975 alumina in such orientation that renders them sensitive to the lateral component of stress during shock loading. A secondary increase in lateral stress, which indicates a decrease in overall shear strength has been observed. It has generally been assumed that such features are damage fronts. Gauges placed at increasing distances from the impact face show that the damage front penetrates less than 5 mm. It is believed that interactions with grain boundaries impede the fronts progress. With increasing impact stress, results show that the velocity of the damage front increases until failure occurs in the main shock itself. Such behaviour has been observed in other brittle materials such as silicon carbide and glasses.