The use of the tank was primarily based on the assumption that, once they were able to eliminate the German trench lines with their machine gun and Infantry support gun positions, the Allied infantry would follow and secure the breach, and the cavalry would exploit the breach in the trench lines by attacking into the depth of German-held territory, eventually capturing the field artillery positions and interdicting logistics and reserves being brought up from the rear areas. Naval crews initially used to operate the installed naval guns and machine guns were replaced with Army personnel who were more aware of the infantry tactics with which the tanks were intended to cooperate. However, there was no means of communication between the tank's crew and the accompanying infantry, or between the tanks participating in combat. Radios were not yet portable or robust enough to be mounted in a tank, although Morse Code transmitters were installed in some Mark IVs at Cambrai as messaging vehicles. Attaching a field telephone to the rear would become a practice only during the next war. With greater use of tanks by both sides it was realized that the accompanying infantry could be forced to ground by ambush fire, thus separating them from the tanks, which would continue to advance, eventually finding themselves exposed to close-assaults by German infantry and sappers.