Infantry operations were usually, if not always, within artillery range. Their depth was also affected by the threat of interception while withdrawing, greater when the Indonesian troop density was higher as it was in the areas south of Kuching. Another constraint was the limited range of man-pack VHF radios A41 & 42, (copies of AN/PRC 9 & 10) and mountainous terrain in some areas. However, A510, an Australian made small HF radio using continuous wave (i.e. Morse code) was used in some areas and new A13 HF radios appeared in early 1966.