Tactical radio communications used in military applications hasstrict requirements regarding security and has to be operable inrough environments in which there may be disturbances and disruptionson a radio link. The performance of the Secure CommunicationInteroperability Protocol (SCIP) operating in an asynchronouscommunication network with various levels of packet loss isinvestigated and found inadequate mainly due to problems withcryptographic synchronization between the transmitting and receivingunits. The introduction of additional counter data to each datapacket remedies this problem and allows the receiving units to fillthe holes left by packet losses with filler packets, maintainingsynchronization. The audio quality can then be measured using thePerceptual Evaluation of Speech Quality (PESQ) algorithm.Measurements are performed in an emulated radio link with aconfigurable packet loss ratio developed by Saab. The results showthat parts of SCIP can be used alongside the counter solution withoutimpacting the audio quality. The insertion of filler packets is shownto have a positive effect on the audio quality, while aggregation ofpackets to conserve transmission data rate is shown to have anegative effect.