Refractory pyrolytic carbides were investigated as erosion resistant barriers on the surface of rocket nozzles, specifically for Polaris nozzles with advanced propellants. A mixture of reactant gases composed of a metal halide and a hydrocarbon was developed for coatings of TaC, HfC and NbC on graphite substrates. High density, single phase, impervious carbide coatings were produced which are intimately bonded to their substrate. Special graphites are required with coefficients of thermal expansion compatible with the carbides. Pyrolytic TaCand NbC-coated rocket nozzle inserts resisted erosion. Partial failures, in term of removal of the coatings in the exit cone section of the nozzles, appeared to be caused by thermal stresses or from structural changes in the substrate material. Thermal shock does not appear to be a problem when these coatings are employed. The feasibility of producing full scale rocket nozzles with surface coatings of pyrolytic carbides was also demonstrated.