The final test was duly carried out, that of Artillery Co-operation. A short distance from the depot a dummy battery of guns was stationed and at a position in tie far corner of the aerodrome, was an object upon which imaginary artillery fire was to be directed. These positions were marked on the map carried by the pilot undergoing the test. All messages were carried out in code and sent from the air by wireless in morse.
As soon as the machine had reached its requisite height, when the pilot had located the target, he wirelessed to the battery, whilst flying towards it '"Are you receiving my signals?" and waited for a ground signal to be exposed in answer.
These ground strips were made of white linen and positioned to represent various letters viz. "L2 might mean "Yes" or "K", "No"- and soforth. Under service conditions, a pilot when patrolling a certain sector of the front, would possibly spot a target (such as a battery of guns, moving troops, etc.) upon which he desired to direct suitable artillery fire. Each of the batteries of our artillery possessed its own code calling up sign, e.g. 60 pounder battery might be "B.E.", a six inch howitzer battery, "R.N.", etc. and according to the type of gun it was desired to engage, so the pilot would utilise the necessary code letters to call up the requisite battery.
In addition to this, each machine had its code number so that the battery would know the flight carrying out the shoot. As soon as the pilot had received the signal that his own signals were being received, he wirelessed the position of the target, which he had worked out from his map, and this message he repeated and followed it up with the coded question - "Are you ready to fire?". An example of the routine is as follows (ficticious code letters are used) –
Machine: A.B.1 Battery Code: R.N. Message: Are you receiving my signals B.Machine: A.B.1 Battery Code: R.N. Message: Position of target P64L39
The complete message – AB1RNP64L39MBattery answer – L.
The shoot then commenced. The pilot flew towards the battery and wirelessed the order to fire, turned and flew towards the target to observe the burst of the exploding shell. His next duty was to send down the correction, preceeding this with the code prefixes. For the purpose of such correction, an imaginary clock face was, drawn round the target, with twelve o'clock due North, calculated by reference to the machine's compass.
Imaginary circles were pictured at various distances from the centre, viz. first ring 50 yards, second one, a hundred yards, third two hundred and fifty yards, etc and called A.,B. and C, etc; the position of a bursting shell was calculated thereby. For instance, a shell exploding fifty yards North of the target would receive a correction 12A, or if to the east, 3A, and a pilot sending a complete correction, including code prefixes, would transmit AB1RNL2A.
When the burst had been observed, the pilot turned the machine, flew towards the battery whilst the correction was wirelessed, and repeated the order to fire; this continued until a direct hit was obtained.
At times, the pilot was called upon to carry out a shoot with two batteries upon different targets, which duty was by no means an easy one; the bursts of two lots of shells had to be observed and corrections sent down with the code prefixes of the various batteries being utilized. During such operations, the pilot was generally subjected to anti-aircraft fire from enemy guns and in addition, had to be prepared to resist an attack by enemy machines.