Halide gases, such as Cl-2, IBr, or ICl, are common etchant species for the etching of III nitrides and other compound semiconductor materials in plasma etching processes. We have investigated the Ga+ focused ion beam milling of GaN in conjunction with gas-assisted etching (GAE) by halide gases I-2 and XeF2. We have observed that I-2 and XeF2 GAE with a 30 keV Ga+ ion beam leads to significantly enhanced GaN etch rates. When these gases are utilized with appropriate ion beam scan strategies (such as ion beam current, beam dwell time, and beam overlap), we have measured GaN etch rate enhancements of 6 X to 9 X and 2 X to 3 X faster for I-2 and XeF2, respectively.