These wireless messages were “tapped” by our compass stations, and it was discovered that two of these stations could get a cross-bearing on any machines registering for the enemy artillery. By linking up the compass station with an aerodrome by telephone, it was possible to send off a patrol of scouts to chase off or destroy the artillery machine as soon as he began to send down fire signals, i.e. as soon as he was actually directing the fire of the enemy batteries. This was useful, though exhausting work for pilots; for the Hun, who did his registration chiefly in the morning, when the sun was behind him in the east, usually saw the scouts coming before they saw him, and turned and dived three or four miles back behind his own lines, where it was very difficult to attack him, even if he was visible, which usually he was not, as our scouts were looking for a machine at five or six thousand feet in a certain place, whereas it was probably at that moment at a height of 1,500 feet some five miles east of the bearing given. As soon, therefore, as the scouts, seeing nothing, turned back to return to the aerodrome, the Hun swung up again and resumed his registration. The British pilots, on returning to their aerodrome, would find an irate squadron commander who had just got a telephone message from the compass station to say that V.K., or whatever the call sign used by that particular machine might be, was working again quite happily, and, “What the devil was 60’s patrol doing, anyhow?” Off the wretched patrol had to go again, only to go through the same performance. It is only fair to say, however, that they did get a good many two-seaters in this way, though the main result was, perhaps, seen rather in the enormously decreased amount of artillery observation the Germans were enabled to do, than in hostile artillery machines shot down by us.
This work, however, was genuinely exhausting, as in order efficiently to answer the compass calls, as they were termed, three or four pilots always had to be standing by to leap into their machines and be off the ground, in formation, inside of two minutes. Nevertheless, they became extraordinarily smart at this manœuvre, and answered to the hunting horn--doubled blasts of which were the signal at that time--as keenly as a fashionable pack of foxhounds. Only those who know how irritating a thing an aero engine can be when you are in a hurry to start can appreciate the high standard of efficiency attained by 60’s mechanics, which made it almost a certainty that the 120 seconds limit would not be exceeded.