The development of the German fighting airplanes had constantly progressed during 1915. Now, early in 1916, they appeared at Verdun, more homogeneous and better trained, and in possession of a series of new machines: small, one-seated biplanes (Albatros, Halberstadt, new Fokker, and Ago), with a fixed motor of 165-175 H.P. (Mercedes, and more rarely Benz and Argus), and two stationary machine-guns firing through the propeller. These chasing escadrilles (_Jagdstaffeln_) are essentially fighting units. Each _Jagdstaffel_ comprises eighteen airplanes, and sometimes twenty-two, four of which are reserves. These airplanes do not generally travel alone, at least when they have to leave their lines, but fly in groups (_Ketten_) of five each, one of them serving as guide (_Kettenfuhrer_), and conducted by the most experienced pilot, regardless of rank. German aviation tactics seek more and more to avoid solitary combat and replace it by squadron fighting, or to surprise an isolated enemy by a squadron, like an attack of sparrow-hawks upon an eagle. Ever since the establishment of our first autonomous group of fighting airplanes, which figured in the Artois offensives in May, 1915, but which did not take the offensive (having their cantonments in the barriers and limiting themselves to keeping off the enemy and cruising above our lines and often behind them), our fighting airplanes gradually overcame prejudice. They were not, it is true, so promptly brought to perfection as our army corps airplanes, which proved so useful in the Champagne campaign of September, 1915; but it was admitted that the aerial combat should not be regarded as a result of mere chance, but as inevitable, and that it constituted, first, a protection, and afterwards an effective obstruction to an enemy forbidden to make raids in our aerial domain. The next German offensive--against Verdun--had been foreseen. In consequence, the staff had organized a safety service to avoid all surprise by the enemy, to meet attacks, and prepare the way for the reinforcing troops. But the violence of the Verdun offensive exceeded all expectations.