Derek Daventry's period off duty was of short duration. In the circumstances he reckoned himself lucky to have twelve hours, most of which he spent in sleeping soundly. In those strenuous times, when every available man and machine had to spend hours in the air with but brief intervals of rest, it was only through sheer exhaustion that pilots and observers were excused duty. He was off again at five in the morning, flying in another EG machine, almost identical with his much-regretted No. 19. The biplanes composing the "flight" were ordered to harass the Germans holding a series of defensive works at a distance of about five miles farther back than the ground captured by the tanks on the previous day. In the present phase of the operations the employment of tanks was out of the question. Tanks are capable of surmounting many obstacles; those they cannot surmount they can frequently demolish; but the mastodons have their limits. They don't like marshy, boggy ground; while a canal or river offers an impassable barrier unless a bridge is available. Eight hundred yards in front of the Huns' position ran a broad canal, seventy-four feet in width and six feet in depth. Every swing-bridge had been blown up and the lock-gates destroyed. Earlier in the day British and French infantry, under cover of a strong artillery-barrage, had succeeded in crossing the canal by means of pontoons, and had established themselves securely on the opposite bank; but so severe was the German machine-gun fire that the advance was held up and the troops compelled to dig themselves in. Already thousands of sand-bags were being dropped into the canal to form a means of getting the tanks across, but a considerable time would necessarily elapse before the work, carried out under fire, could be perfected; while it was evident, from the determined resistance of the enemy, that the attackers were being held up by a crack Prussian division. The attacking 'planes flew well to the east of their objective, and, turning, bore down, with the light of the rising sun well behind them. It meant flying against the wind, but when engaged in raking a trench, speed is not of paramount importance. Five thousand feet above the machine-gunning biplanes hovered a squadron of battleplanes, ready at the first appearance of a Hun to swoop down and wipe him out of existence should he have the temerity to attack. But not a German machine showed itself, and the huge battleplanes had to be content with affording moral support to their smaller sisters of the air. The German infantry had no stomach for the swift death that threatened from the sky. At the first appearance of the biplanes, the field-greys promptly abandoned their fire-steps and dived into their dug-outs. This was hardly what the British airmen expected, since it is to little purpose to fire thousands of rounds of small-arm ammunition into an empty trench.