<p>Diametrical compression tests were performed on cylindrical ice single crystals with typical <i>c</i>-axis orientations under nominally constant strain rates. Strain evolution was tracked using digital image correlation, and crack morphology was observed under cross-polarized light to investigate the effects of <i>c</i>-axis orientation and strain rate on plastic deformation and failure behavior of ice single crystals. The results showed that ice single crystals exhibited pronounced anisotropic and rate-dependent mechanical characteristics. Heterogeneous plastic deformation is primarily manifested as localized strain bands aligned with basal dislocation slip, with the morphology, intensity, and width of these bands strongly influenced by <i>c</i>-axis orientation. Rate-sensitivity exponents for basal and non-basal slip were determined from the nearly log-linear relationship between specimen load and strain rate in the ductile regime. As the strain rate increased, the failure mode transitioned from ductile to splitting failure, with crack morphology depending on <i>c</i>-axis orientation: ductile failure occurred mainly via shear cracks along the basal plane in basal slip-favored orientations, while splitting failure appeared as tensile cracks parallel to the <i>c</i>-axis in small-angle specimens and as cleavage cracks parallel to the basal plane in large-angle specimens.</p>