[en] Au films have been irradiated in the Harwell 1.0 MeV electron microscope at electron energies in the range 0.4 to 1.15 MeV, below the threshold energy for Frenkel pair production in the bulk. Under irradiation, films were observed to undergo thinning at rates of up to typically 0.4 A sec^-1 at 1.15 MeV (increasing with electron energy), which can be explained by sputtering of Au atoms by electrons from the exit foil surface. In addition to sputtering, films irradiated at low temperatures and subsequently annealed were found to contain high densities of vacancy stacking fault tetrahedra. Experimental observations of the growth of stacking fault tetrahedra in Au at sub-threshold energies are reported. Evidence is given that this sub-threshold damage is caused by dynamic vacancy injection into Au as a result of sputtering. The possible mechanisms of vacancy injection are discussed