4.2 p.m. A very little short. Fire. Fire. 4.4 p.m. Fire again. Fire again. 4.12 p.m. A little short; line O.K. 4.15 p.m. Short. Over, over and a little left. 4.20 p.m. You were just between two batteries. Search two hundred yards each side of your last shot. Range O.K. 4.22 p.m. You have them. 4.26 p.m. Hit. Hit. Hit. 4.32 p.m. About 50 yards short and to the right. 4.37 p.m. Your last shot in the middle of 3 batteries in action; search all round within 300 yards of your last shot and you have them. 4.42 p.m. I am coming home now. The later signals directing artillery fire were not so full of colour as these early messages. They consisted of code letters. The clock code for signalling the results of artillery fire was first used in 1915 and afterwards generally throughout the war. The target was taken as the centre of a clock and imaginary lines were circumscribed around it at distances of 10, 25, 50, 100, 200, 300, 400, and 500 yards. These lines were lettered Y, Z, A, B, C, D, E, F, respectively. Twelve o'clock was always taken as true north from the target and the remaining hours accordingly. An observer noted the fall of the rounds with reference to the imaginary circles and clock-hours and signalled the result, for instance, as Y 4, or C 6. A direct hit was O.K, and there were other signals. Messages from the battery or any other ground station were signalled to the observer in the aeroplane by means of white strips which were laid out on the ground to form the letters of a code.