We report on in situ space charge spectroscopy measurements on low-temperature proton-bombarded n-type gallium nitride thin film samples. The scope of this study was to investigate the introduction and annealing dynamics of radiation-induced lattice damage. Using optical excitation allowed for the detection of electronic defect states in the entire GaN bandgap and to detect unstable primary defects that would have been invisible in thermal space charge spectroscopic measurements. The introduction of compensating acceptor-like primary defects by the bombardment was observed and manifested as a decrease in the sample capacitance. After the bombardment the concentrations of deep-levels and acceptor states were monitored by deep-level transient spectroscopy and photo-capacitance measurements while the temperature was increased. It was found that annealing and reactions of primary bombardment-induced defects occurs even below room-temperature which might account for the radiation-hardness of GaN.