Ceramic matrix composites (CMCs) are structural materials, which have useful properties that combine high strength at high temperatures with moderate toughness. Carbon fibers within a matrix of carbon and silicon carbide, called C/C–SiC, are a particular class of CMC noted for their high oxidation resistance. Here we use a combination of four-point bending and X-ray radiography, to study the mechanical failure of C/C-SiC CMCs. Correlating X-ray radiographic and load/displacement curve data reveals that the fiber bundles act to slow down crack propagation during four-point bending tests. We attribute this to the fact that strain energy is expended in breaking these fibers and in pulling fiber bundles out of the surrounding matrix material. In addition, we find that the local distribution and concentration of SiC plays an important role in reducing the toughness of the material.