By the Summer of 1916, however, we had adapted the "synchronizing gear" to our machine guns, enabling them to be fired through the propeller; while aircraft engines developed much greater power and full allowance was made for all equipment carried. From that time the development of our single-seater fighters was steadily progressive. One of the first of these was the Sopwith "Pup," which had a speed of 106-1/2 miles an hour at 6,500 feet, climbed 10,000 feet in just over 14 minutes, and could attain a ceiling of 17,500 feet. In 1917 appeared the Sopwith "Camel," a typical example of this type, which was simple, stable, easily controllable and possessed two guns. It had a speed of 121 miles an hour at 10,000 feet, to which height it could climb in under 10-1/2 minutes, and a ceiling of 23,000 feet. The Martinsyde F.4, embodying further improvements, was not ready in time for active service. While the single-seater tractor was developing for purely offensive action, the two-seater fighter, of which the field of view, man[oe]uvrability and general performance were being improved, retained its utility as a reconnaissance machine. In 1916 the "pusher" type was superseded by the Sopwith "1-1/2 Strutter" armed with a synchronized Vickers gun, which for its 130 horse-power was never surpassed. The pilot was close to the engine and had a good view of the ground, while the gunner was placed behind him with a rotary Lewis gun turret. Early in 1917 these qualities were further developed in the Bristol Fighter. With the advent of these improved types the B.E.2c was relegated to the work of artillery co-operation, until superseded by the B.E.2e. Towards the end of 1916 appeared the R.E.8 with a Vickers synchronized gun and a Lewis gun, which after many vicissitudes became the standard machine for artillery work. Systematic bombing was practised by nearly all types of machines, but real accuracy was never obtained. Thus, the B.E.2c was first used in formations, but with a full load of bombs it could not carry an observer, and its moderate speed left it an easy prey to hostile fighters. Early in 1916 appeared the Martinsyde single-seater bomber with an endurance of 4-1/2 hours, and in 1917 the D.H.4 which was much used for day-bombing. The F.E.2b pusher, discarded as a fighting machine, became the principal night-bomber.