Scouts generally operate in pairs, for if it is impossible to signal back from the ships, one continues the work while the other makes a signaling report from such point or points in the rear as will make the information useful. The next duty is to protect the scouts from interference. This work is carried on by the large ships, which are usually provided with rapid fire guns. They need not, necessarily, be speedy, for they are to keep in touch with the speedy scout ships, the latter of which sail around over a small area so the observations can be carried on as leisurely as possible. Third come the bomb-throwers, usually heavy-powered machines, generally not armed, as all the carrying power is devoted to the transportation of bombs. These are also guarded by the heavily armed machines. Sometimes, as in the case of the Farman machine, which the lieutenant used, they were used for scouting, and were also serviceable for fighting purposes. In the early period of the war there were not many pilots capable of doing the duty required in all branches of the service. It was frequently the case that the aviator would command a ship with a gun on it and do double duty, acting as scout, or he would chase and fight an enemy, manipulating the gun while manoeuvering the machine. It was the sort of duty in which Lieutenant Guyon was engaged at the time he was promoted to the command, and supplied with the new type of machine. Naturally, as commander of the squadron, he was at liberty to take any one he desired in his flights, and as he had a real affection for the boys, he took delight in having them accompany him on many of his exploits. It was the custom for the lieutenant to entrust the piloting of the machine to one of the boys, while he acted as a scout. Frequently Ralph would perform this duty, while Alfred, with his camera engaged, under the direction of the lieutenant, taking such photos as were deemed necessary to supplement the Department maps. Thus over a month was spent in scouting duty, and, as the weather became somewhat chilly, especially in the evenings, they never went aloft without being well muffled up. One morning the lieutenant called out to the boys that they were likely to have a busy day before them, as the weather was unusually mild for the season. When they arrived at the hangar the machine was already out of the shed, and the lieutenant was busy with the charts in consultation with the officer of the day. Evidently something unusual was afoot, for they waited more than an hour before the lieutenant re-appeared. "You might wrap up well," he said. "I have ordered a good luncheon, as we shall have a good long scouting area to cover." "Which way are we going?" asked Ralph. "Directly across the city, and then to the east. There is some unusually active business going on between this and Metz." "Think I had better load up the camera pretty well, even though it is a little misty," said Alfred.