Beyond this hut are the men's quarters which are deserted at this hour. Across the road is the workshop or repair factory which, under the eye of "Bill," the engine officer, runs "full blast" from six in the morning to nine or ten at night. Next to this miniature factory is the armorers' hut where all the machine guns are overhauled daily, ammunition tested as regards rims, sunken caps, etc., and every possible precaution taken to render the guns thoroughly efficient. Near by are the huge, camouflaged hangars, or buildings containing the aeroplanes. Here the mechanics are "tuning up" the engines; the riggers are trueing up the aeroplanes, tightening a flying wire here, loosening a landing wire there, testing controls; in fact, doing all that scientific knowledge and care can do to reduce the chance of accident from mechanical imperfection. And upon these patriotic, scientific mechanics, working for their country and their ideals and recompensed from a pecuniary point of view with a shilling or two a day, rested to a large extent, the lives of the aviators and the success of their various adventures. Back of the hangars and near the officers' quarters is the squadron office. Here are several clerks constantly engaged in recording all the details relating to the men's pay, their military records, their issues of clothes, blankets, etc.,--in fact, recording and filing everything dealing with the squadron's activities. Next to the squadron office is the large map-room. If a squadron on active service can be compared to the human body, the map-room is the brain of the squadron, for here is kept all the information essential to the aviators. On one wall is a huge map of the whole war zone from the coast to the Swiss border. On this the front-line trenches are accurately marked, with their changes made from day to day. On the wall next to this map and at right angles to it, is a large-scale map of the entire region over which the squadron operates. On this map are numerous conventional markings which would have no meaning to the casual observer. [Illustration: THE PATRIOTIC, SCIENTIFIC MECHANICS] In maps of the enemy territory are hundreds of red drawing-pins. These mark the positions of enemy anti-aircraft batteries. As soon as information is received of the movement of one of these batteries, the pin which represents that particular battery is moved to the new position. Small yellow squares or oblongs with minute black marks represent the enemy aerodromes and hangars. These conventional signs correspond accurately to the aerial photographs of these aerodromes.