After climbing up a ladder to their respective positions, the aviators made a final survey of the machine on the reliability of which depended the success of their adventure. The engines were again run up to see that they gave the proper revolutions, the gauges inspected, the controls tested, and the return spring of each gun weighed. When thoroughly satisfied, each aviator took his place and his pilot signalled for the "chocks" to be withdrawn from in front of the wheels. While the aviators carried on this final inspection of their machines, the aerodrome officer, stationed on a high platform situated in one corner of the field, awaited the signal to light the "landing T"; i.e., a huge "T" of electric lights headed into the wind, which shows to the aviators the taking-off and landing path. Each machine is given its respective letter for the day, which is flashed in Morse code on the navigation lights by the aviator when ready to leave the ground; he then awaits an answer from the directing stand. Simultaneously with the lighting up of the huge "landing T," the letter flashed from the first machine ready is repeated by the signal officer. The answer received, the machine taxies across the aerodrome to the starting-point, turns, hurtles down the flare-path and leaves the ground at the head of the "T." Under this simple method of direction I have seen twenty aeroplanes leave an aerodrome on a pitch-black night in twelve minutes without a single mishap. On leaving the ground the aeroplanes fly dead into the wind for a couple of miles, circle back to the left around the aerodrome, and head into the wind again until the height at which the flight is to be carried out is reached. The first aeroplane to reach this height passes directly over the aerodrome and then steers a course to the first lighthouse. A comparison of this course with the previously figured course, and a comparison of the previously calculated ground speed with the time taken to travel from the aerodrome to the lighthouse enables the aviators, by the use of instruments and a few simple calculations, to gauge their drift. This process is continued on another course to the next lighthouse and the previously tested direction and velocity of wind are accurately checked in this way and future courses altered accordingly. These calculations are all important to the long-distance night bomber, for although roads show up in the moonlight like white threads, they are too numerous and interwoven to be followed for great distances, and although rivers and lakes look like silver ribbons and blotches, the moon may be obscured at any moment or the ground itself may be obliterated by low clouds or mist. Accuracy in aerial navigation, therefore, is of the utmost importance in long-distance night flying.