The whole equipment is so built that we used to set it up ready for work in from three to five minutes. The operators then adjusted their head-phones and were ready to _tune-in_ the incoming signals from the airplane as soon as it should come in sight. You see, our detail on the ground only received wireless signals from the airplane while the operator in it, or _observer_ as he is called, only sent wireless signals. This one sided arrangement had to be used because the propeller makes so much noise that the operator in the airplane would have trouble in reading the signals. In order to signal to the airplane as she flew above us we used a system of _panels_. [Illustration: “THE AIRPLANE SIGNALLED DOWN TO US IN CODE”] This consists of a large piece of white cloth about twelve feet square spread out on the ground and three strips of white cloth twelve feet long and a couple of feet wide. These strips are laid in different positions relative to the square and each position has a number that means an order which the observer in the airplane also knows. Further a small black square about eighteen inches on the side is placed on the big white square so that the observer can tell which battalion the outfit belongs to. The different positions of the strips and square are given numbers and the panelmen as well as the observer know what order each number means. As the panels can be arranged in twenty-seven different positions it is just about as hard to learn the panel code as it is the Morse alphabet. Now as soon as the wireless apparatus has been set up the panelmen put out their big square and one strip at the end of it, and when the airplane comes close enough to see the panels he knows that we want him to _designate_, that is to name the target which the battery is to fire at. This he sends to us by wireless and our operators write it down. While our detail was setting up the wireless apparatus, the _telephone detail_ from our outfit had run a _wire line_ from our B. C. station to the batteries which are several hundred yards ahead of us. When our operators get the target, or _pin-point_ as it is called, from the observer in the airplane, he (the operator) phones it to the battery commander who orders the guns set for it. The airplane then signals down to us in code and asks “is the battery ready?” The telephone man tells us that the battery is ready and the panelmen put out No. 5, which means “the battery is ready.” The airplane observer sends down “_fire_,” our operators yell the order to the telephone man who in turn shouts it into the mouthpiece of his ’phone; the ’phone operator at the battery end informs the Battery Commander and he gives the order when the guns are fired either by _piece_, that is one at a time, or by _salvo_, which is all at once.