rcraft. At that time, it was reckoned that effective aerial
photography ceased at 6,000 feet, while bomb-dropping from 7,000-8,000
feet was reckoned uncertain except in the case of a very large target.
The improvement in anti-aircraft devices went on, and by May of 1916, an
aeroplane was not safe under 15,000 feet, while anti-aircraft shells had
fuses capable of being set to over 20,000 feet, and bombing from 15,000
and 16,000 feet was common. It was not till later that Allied pilots
demonstrated the safety that lies in flying very near the ground, this
owing to the fact that, when flying swiftly at a very low altitude, the
machine is out of sight almost before it can be aimed at.

The Battle of the Somme and the clearing of the air preliminary to that
operation brought the fighting aeroplane pure and simple with them.
Formations of fighting planes preceded reconnaissance craft in order
to clear German machines and observation balloons out of the sky and to
watch and keep down any further enemy formations that might attempt
to interfere with Allied observation work. The German reply to this
consisted in the formation of the Flying Circus, of which Captain Baron
von Richthofen's was a good example. Each circus consisted of a large
formation of speedy machines, built specially for fighting and manned
by the best of the German pilots. These were sent to attack at any point
along the line where the Allies had got a decided superiority.

The trick flying of pre-war days soon became an everyday matter; Pegoud
astonished the aviation world before the War by first looping the loop,
but, before three years of hostilities had elapsed, looping was part of
the training of practically every pilot, while the spinning nose dive,
originally considered fatal, was mastered, and the tail slide, which
consisted of a machine rising nose upward in the air and falling back on
its tail, became one of the easiest 'stunts' in the pilot's repertoire.
Inherent stability was gradually improved, and, from 1916 onward,
practically every pilot could carry on with his machine-gun or camera
and trust to his machine to fly itself until he was free to attend to
it. There was more than one story of a machine coming safely to earth
and making good landing on its own account with the pilot dead in his
cock-pit.

Toward the end of the War, the Independent Air Force was formed as a
branch of the R.A.F. with a view to bombing German bases and devoting
its att