A boron carbide composite body produced by an infiltration process that possesses high mechanical strength, high hardness and high stiffness has applications in such diverse industries as precision equipment and ballistic armor. In one embodiment, the composite material features a boron carbide filler or reinforcement phase, and a silicon carbide matrix produced by the reactive infiltration of an infiltrant having a silicon component with a porous mass having a reactable carbonaceous component. In an alternate embodiment, the infiltration can be caused to occur in the absence of the reactable carbonaceous component, e.g., to produce "siliconized boron carbide". Potential deleterious reaction of the boron carbide with silicon during infiltration is suppressed by alloying or dissolving a source of boron, or a source of carbon, or preferably both boron and carbon into the silicon prior to contact of the silicon infiltrant with the boron carbide. In a preferred embodiment of the invention related specifically to armor, good ballistic performance can be advanced by loading the porous mass or preform to be infiltrated to a high degree with one or more hard fillers such as boron carbide, and by limiting the size of the morphological features, particularly the ceramic phases, making up the composite body. The instant reaction-bonded boron carbide (RBBC) composite bodies are at least comparable in ballistic performance to current boron carbide armor ceramics but feature lower cost and higher volume manufacturing methods, e.g., infiltration techniques.