<P> In the early days of the war, generals tried to direct tactics from headquarters many miles from the front, with messages being carried back and forth by couriers on motorcycles . It was soon realized that more immediate methods of communication were needed . </P> <P> Radio sets of the period were too heavy to carry into battle, and phone lines laid were quickly broken . Runners, flashing lights, and mirrors were often used instead; dogs were also used, though they were only used occasionally as troops tended to adopt them as pets and men would volunteer to go as runners in the dog's place . There were also aircraft (called "contact patrols") that could carry messages between headquarters and forward positions, sometimes dropping their messages without landing . </P> <P> The new long - range artillery developed just before the war now had to fire at positions it could not see . Typical tactics were to pound the enemy front lines and then stop to let infantry move forward, hoping that the enemy line was broken, though it rarely was . The lifting and then the creeping barrage were developed to keep artillery fire landing directly in front of the infantry "as it advanced". Communications being impossible, the danger was that the barrage would move too fast--losing the protection--or too slowly--holding up the advance . </P> <P> There were also countermeasures to these artillery tactics: by aiming a counter barrage directly behind an enemy's creeping barrage, one could target the infantry that was following the creeping barrage . Microphones (Sound ranging) were used to triangulate the position of enemy guns and engage in counter-battery fire . Muzzle flashes of guns could also be spotted and used to target enemy artillery . </P>

Which of the following was not a new weapon or new method of warfare used during world war i