rked the position of enemy anti-aircraft
batteries, aerodromes, and balloon barrages; but on our side of the
lines there were large areas marked in red to indicate what was called
"prohibited areas"; i.e., areas over which no aeroplane, Allied or
enemy, could fly without being subjected to the fire of our
anti-aircraft batteries.

There were also white drawing-pins, each bearing a letter, placed at
irregular intervals. These located accurately the position of small
lighthouses which are usually about fifteen miles apart and from three
to ten miles back of the front-line trenches; the letter marked on each
drawing-pin designates the letter flashed in Morse code by that
particular lighthouse. This system of signals, used by the British to
direct their night aviators to their aerodromes when returning from a
raid, had but two great faults. In the first place, the signal was
obliterated by low clouds and mist. In the second place, the flash of
the light only carried a few miles even under the best conditions. On
the other hand, the letters which the lighthouses flashed could be
readily changed and consequently were of very little assistance to Hun
aviators.

On the third wall of the map-room are aerial photographs of enemy
aerodromes, railway stations, sidings, etc., and large-scale plans of
German towns and factories.

On the table in the centre of the room are the various instruments by
the aid of which the aviators are enabled to figure out their magnetic
courses. Every afternoon the map-room is crowded with aviators. Here all
the plans for the raid are made, the courses figured and marked on
individual charts, the photographs or plans of targets studied and the
best methods of approaching the target discussed. In the evening the
wind soundings made by the meteorological expert are reported and again
the map-room is crowded with aviators figuring out "drift" and "ground
speed" and making out charts which will facilitate their navigation when
in the air.

CHAPTER IV

A NIGHT RAID

Every precaution having been taken, the engines run, the controls
tested, the compasses swung, the courses made out, the charts prepared,
and the drift figured, the Bedouins sat down to dinner free from care or
worry. The dinner hour was always set, winter or summer, at least two
hours before the night's raid was to start.

A guest of the Bedouin mess on the night of an important raid would have
been surprised if told that the