ated with
the attacking force; Major Brooke-Popham was with the defence at
Cambridge. Operations started at six o'clock on the morning of Monday,
the 16th of September. At a conference on Sunday afternoon, General
Briggs, who commanded the cavalry on the side of the defence, told
General Grierson that the forces were far apart, and he could not hope
to bring in any definite information till Tuesday. General Grierson was
then reminded by his chief staff officer that he had some aeroplanes.
'Do you think the aeroplanes could do anything?' he asked of Major
Brooke-Popham, and on hearing that they could, ordered them to get out,
'and if you see anything, let us know.' Monday morning was fine and
clear; the aeroplanes started at six o'clock; soon after nine o'clock
they supplied General Grierson with complete, accurate, and detailed
information concerning the disposition of all the enemy troops. During
the rest of the manoeuvres he based his plans on information from the
air. On his left flank there were only two roads by which the enemy
could advance; he left this flank entirely unguarded, keeping one
aeroplane in continual observation above the two roads, and so was able
to concentrate the whole of his forces at the decisive point. In the
course of a few days the aeroplanes rose into such esteem that they were
asked to verify information which had been brought in by the cavalry.

Air Commodore C. A. H. Longcroft, who flew in Major Burke's squadron on
the attacking side, has kindly set down some of his memories of this
time. The work of the Flying Corps, he says, was impeded by the enormous
crowds which used to collect round the hangars. But the weather was
good, and it was soon found that no considerable body of troops could
move without being seen from the air. To avoid observation the troops
moved on either side of the road, under the hedges. They even practised
a primitive sort of camouflage, covering wagons and guns with branches
of trees, which, while they were on the road, made them more conspicuous
than ever. This first experience of moving warfare taught many lessons.
The difficulty of communication between pilot and observer when the
voice is drowned in the noise of the engine was met by devising a code
of signals, and many of these signals continued in use throughout the
war, after speaking-tubes had been fitted to machines. The selection of
landing grounds when moving camp, the methods of parking aeroplanes in
t