Technical progress during the war often unfortunately involved the loss of valuable lives, as for instance those of Professor Hopkinson and Busk, to both of whom heavy debts of gratitude are owed, but gradually obstacle after obstacle, problem after problem, was successfully tackled by our designers and constructors. With a view to enlarging the field of observation, staggered planes were introduced in the B.E.2c. This machine also proved that it was possible to calculate the degree of stability and thus paved the way for the design of aeroplanes with indifference to stability and increased man[oe]uvrability for fighting purposes, or with great inherent stability for bombing. During 1915 the B.E.2c was used for all purposes, but the extra loading involved by the increasing use of aeroplanes for bombing and fighting caused a decrease in the rate of speed and climb, and our aeroplanes were temporarily inferior in fighting power to the Fokker. The necessity of preventing the enemy obtaining information soon led to the development of air fighting. At the beginning of the war the sole armament of aeroplanes was the rifle or revolver. The machine gun soon followed, but its use in tractor machines was impracticable on account of the danger of hitting the airscrew. The first "fighters" were therefore two-seater pushers, such as the "Short-horn" Maurice Farmans which, though not designed for fighting, and too slow to chase enemy aircraft, were the first to be fitted with Lewis guns, and F.E.'s, the first machine designed specifically for fighting, with the machine-gun operator in front of the pilot. These "pusher" fighters had an excellent field of view and fire forwards, but suffered from lack of speed and a large "blind" area to the rear. On the other hand, the single-seater tractors were potentially the superior fighters, and in order to protect the blades of the airscrew the French were the first to use deflector blades on them in tractor machines. Our early single-seater tractors were fitted with a Lewis gun fixed so as to fire over or at the side of the airscrew and actuated by a bowden wire, the most efficient, though not the most numerous, fighting machines at the end of 1915 being the Bristol Scouts.