The effect of 700 keV In implantation and subsequent annealing on GaN was studied by Rutherford Backscattering spectroscopy, Raman spectroscopy and nano-indentation as a function of the ion fluence (F) ranging from 5x10(13) to 1x10(16) cm(-2). Symmetry allowed and disorder activated Raman scattering peaks were analyzed using the spatial correlation model, allowing their assignment to phonon branches of crystalline GaN or defects and the estimation of the corresponding phonon coherence length (L). The L values decrease abruptly at a critical fluence of approximately 2x10(14) cm(-2). After a slight increase in the nano-hardness (H) and reduced elastic modulus (E-r) values at low implantation fluences, they exhibit a steep reduction. These variations are accompanied by changes in the shape of the load-displacement curves, which are indicative of elasto-plastic behavior up to a critical F, whereas they approach the ideal plastic behavior at higher fluences. Annealing at 1000 degrees C of the sample implanted with 1x10(15) ions/cm(2) results in efficient recovery of its structural and nano-mechanical properties. However, annealing of specimens implanted at higher fluences causes partial recovery that starts mainly from the transition region between the heavily damaged and the underlying undamaged GaN. The highly correlated behavior of L, H and E-r on the implantation fluence implies a common origin of the studied effects. (C) 2013 Elsevier B.V. All rights reserved.