The microstructures of sapphire single crystals explosively shocked at pressures of 5, 12, and 23 GPa, with the basal plane perpendicular to the shock wave direction, have been studied using transmission electron microscopy. There was no evidence of microplastic deformation, dislocations or twins, for crystals shocked at 5 GPa. Perfect dislocations with 1010 and ⅓1120 Burgers vectors on the basal planes were observed at the higher pressures. The gliding of 1010 dislocations on the basal plane established the activation of {0001}1010 slip, which has not been experimentally verified previously. In addition to dislocation generation and motion, a significant number of basal twins were observe