After the Battle of the Aisne, which was the turning point in the evolution from the war of movement to trench warfare, pure reconnaissance, though still the basis of air work, tended to become a matter of routine, while many new and specialized forms of it--such as air photography and artillery spotting by wireless--were developed. _Photography._ Though experiments had been made in the problem of photography from the air before the war, principally by Fletcher, Hubbard and Laws, and its value to survey was recognized, it had not become of practical utility. We only took one official camera with us to France on August 13th, 1914, and it was not until September 15th that the first attempt at air photography was made, when five plates were exposed over positions behind the enemy's lines with very imperfect results. Its great value as an aid to observation in trench warfare was, however, very apparent, fresh brains were brought to the task, Moore-Brabazon, Campbell and Dr. Swan, and by the end of the year better success was obtained, though positions even then had to be filled in by the observer with red ink. Experiments at home during 1915 led to a great improvement in lenses, and at the beginning of 1916 air photography was universal. At the Battle of the Somme new enemy positions were photographed as soon as they were seen, and the camera did invaluable work in the reconnaissance of the Hindenburg Line during the German retreat of 1917, and the taking of over a thousand photographs was a daily occurrence. On September 4th, 1917, a record of 1,805 photographs was made. The development of air photography, very remarkable in itself, is even more so when it is remembered that the improvement in enemy anti-aircraft guns drove our machines to carry out their work at altitudes increasing up to 20,000 and even 22,000 feet, at which heights the negatives had to be as distinct as those taken at 4,000 in the earlier days of the war. At the beginning of the Dardanelles operations our apparatus consisted of one camera, a printing frame and a dark room lamp. The first photographs were taken by Butler in April, 1915, from a H. Farman machine at necessarily low altitudes. Butler was wounded in June and was succeeded by Thomson, who alone made 900 exposures and sent in 3,600 prints. In addition to the assistance of air photography to reconnaissance, the war gave it great impetus as the handmaid of survey and mapping. It was, in fact, the only means of mapping or correcting the maps of country held by the enemy, which in certain cases, as at Gallipoli and in Palestine, were very inaccurate.