for the second time within twelve hours derek daventry made a journey by car to le tenetoir aerodrome. on the second occasion it was to give evidence against the airman-spy count hertz von peilfell; but upon arriving at his destination he found that the court-martial had been summoned to no purpose. the prisoner had escaped, and, although his description had been circulated all along the allied front and over the back-areas, the count was still at large.

amongst the british airmen the general tone of expression was one of sympathy—as far as sympathy could be extended to a hun. von peilfell was a crack airman; his r?le of spy was quite in accordance with modern warfare, for both british and french air-craft had frequently landed spies well behind the german lines. it was almost unanimously felt that, if count von peilfell were to fall, a fitting end to him would be in aerial combat. if he fell on territory occupied by the allies he would be buried with full military honours; if on soil temporarily held by the huns, then a british aeroplane would doubtless circle over the funeral-party and drop a wreath bearing a tribute to the crack hun flyer's prowess.

but sterner work was on hand. it was a carefully-kept secret that at dawn on the next day following the spy's escape a frontal attack was to be delivered upon the huns, still holding a strongly-fortified section of the line—a front of twenty miles, protected on both flanks by broad canals, and defended by mazes of trenches and barbed-wire entanglements.

once this section were pierced, the whole german line would be in danger. army corps would be practically surrounded and forced to surrender, while a broad wedge would be driven between the huns in flanders and those who were stoutly resisting the franco-american troops in the neighbourhood of metz.

an infantry attack would be too costly. heavy artillery bombardment would give the boches an inkling of what was about to develop. on this account the british guns had of late remained comparatively inactive, in order to lull fritz into a state of false security.

so the assault was to be delivered by tanks, supported by relatively small detachments of infantry, while the r.a. f. were ordered to co-operate to their utmost capacity. every available machine fit for offensive work was to be employed in the operations, the idea being not only to paralyse the huns in the firing-line, but to prevent reinforcements and supplies reaching them. in brief, the whole of a certain german sector was to be wiped out.

at five in the morning, or two hours before dawn, the tanks were to start upon their grim errand. every square foot of ground occupied by the enemy in the coveted sector had been photographed and re-photographed by daring airmen. the work had been efficiently performed, but at a cost, as the long r.a.f. casualty list testified. it was not in the heat of combat that these daring aerial photographers had been shot down, but in the cold, methodical pursuit of an art that the demands of modern warfare had relentlessly absorbed.

with an accurate knowledge of the nature of the terrain the task of the tanks had been rendered fairly straightforward. there were, of course, hidden pitfalls which the almost all-seeing lens of the camera failed to detect: cleverly-camouflaged gun-emplacements and nests of machine-guns that were not shown on the finished photograph-prints; but even here the work of the airman was evident. cryptic markings on the prints gave the staff officers certain clues—an anti-aircraft battery here; a booby-trap there, an observation-post in that place. the science of detecting screened pitfalls was almost as perfect as the skilful art of camouflage.

there were tanks and tanks. the ground trembled under the pulsations of their powerful engines. whippets, male tanks, female tanks, "rolls" tanks capable of doing twenty miles an hour with their 250-h.p. engines; tanks mounting six hundred quick-firers, tanks bristling with machine-guns—a veritable armada of land-ships moving forward in what appeared to be a solid, compact mass.

they moved slowly at first, each section led by an officer on foot towards the as yet invisible german lines. there had been a spell of quietude on this part of the front of late. the huns considered their defensive works so perfect that a frontal attack would be impossible, and, being let severely alone, they had refrained from their usual lavish display of star-shells.

grunting, groaning, coughing; ejecting vile, sulphurous fumes from their noisy exhausts, the steel-clad mastodons ambled onwards until fritz, suddenly aware that danger was at hand, opened a furious fire that threw a dancing, lurid glare upon the crater-pitted plain over which the hordes of tanks surged like a sullen ground-swell beating upon a flat shore. vivid red and white rockets—fritz's s.o.s. signals—soared skywards, an appeal by the field-grey infantry for support from their heavy artillery.

it was at this juncture that derek daventry, one of the host of aerial fighters, found himself flying at a few hundred feet above the boche lines.

in the reflected glare of the rifle- and machine-gun fire he could discern the array of tanks advancing. the slow-moving tanks were in the van, their raison d'être to flatten down the hostile wire and pave a way for the whippets and "twenty-milers" of the land-fleet. machine-gun bullets were rattling against their armoured snouts, while here and there bursts of vivid-red flame gave token that the anti-tank bullets—steel-cored and copper-encased missiles—had put more than one tank out of action.

all this derek took in as the result of a few seconds' flight. then, over the hostile front, his work began. in darkness, save for the intermittent flashes of the guns, the british 'planes sped to and fro. unavoidable collisions brought friends crashing to earth; oft-times the machines were flying blindly through clouds of black, nauseating smoke. rocking, side-slipping, bumping, and banking, the aerial-fleet continued its work in hammering with the land-armada of tanks. machine-gunning, bombing, and dropping poison-gas cylinders, the airmen hovered remorselessly over the now-demoralized boches, while the tanks, surging onwards, beat down acres of barbed-wire and flattened out whole sectors of trenches.

derek had just fired his ninth tray of ammunition when he felt the joy-stick give. a fragment of shell had severed the "nerve-centre" of the biplane, and the 'bus was now practically out of control. a touch upon the rudder-bar turned eg 19 in the direction of "home", but almost immediately the engine "konked". in the darkness it was impossible to see what had happened, but another fragment of shell had lodged fairly in the magneto.

eg 19 had to come down. how she came down depended upon sheer luck, since the skill and nerve of the pilot were useless to avoid the threatened calamity.

derek steeled himself to meet the tremendous crash, but the shock never came. by one of those eccentricities of movement that aerial-craft occasionally perform, the biplane flattened out within twenty feet of the ground, dipped her nose, and then pancaked upon the shelving side of a large shell-crater. without a scratch the pilot scrambled out of the fuselage and gained the ground.

he promptly threw himself at full length in the stiff mud that lay in the bottom of the crater, and listened to the appalling racket overhead. shells of light calibre were screeching and bursting all around, their uproar punctuated by the heavier concussion of aerial-bombs. a crescendo of machine-gun fire added to the deafening roar, while the hail of bullets directed upon the imperturbable tanks sounded like a continuous tattoo.

almost on the lip of the crater a large tank had come to a standstill. two jagged holes in her fantastically-painted sides showed that a hun anti-tank gun had scored direct hits, but whether these had put the mobile fort out of action derek was unable to determine.

while debating whether it would be safer to take cover under the lee of the tank or to remain in the doubtful security of a wide shell-crater, daventry saw the door in the wake of the tank's sponson thrown open, and a couple of mechanics crawl through, followed by a waft of brownish smoke.

at first sight the flying-officer imagined that the men were the sole survivors of the land-ship's crew, but he was mistaken. it was a case of engine failure that had brought the tank to a halt, and since the only means of "cranking-up" was performed from without, the mechanics were risking death in the open in a laudable effort to restart the motors.

even as the men strained frantically at the handle a shell burst within five yards of the tank. one of the mechanics, caught by the direct blast of the explosion, was wiped out of existence; the other, by one of those inexplicable freaks of fortune, escaped with only a slight shock. although only a few inches from his luckless comrade he was evidently in the so-called safety-zone of explosion. slightly dazed, and apparently oblivious of the fact that he had missed death by inches, he sweated at the cranking-handle in a vain attempt to overcome the compression.

acting purely upon impulse, and not taking into account the risk, derek scrambled up the loose mound of earth, against which bullets were burying themselves with a succession of dull thuds. then across the few yards of open ground he ran, and threw himself at the starting-gear.

the mechanic took no notice of the new arrival. his whole mind was set upon his task. even had derek been a boche it is doubtful whether the man would have given him a thought.

"hold out there, mate!" shouted the mechanic, without raising his head. derek grasped the cranking-handle. the other, placing his foot upon the metal, brought his whole weight down. over swung the crank, and with a thunderous roar the powerful motor fired—and continued to do so. through the eddying fumes daventry could discern the mechanic, with hunched shoulders, stumbling towards the still open door.

"this is a stunt that will suit me," exclaimed the young officer. "a change is as good as a rest." the next thing he remembered was barking his shins on the sharp, metallic edge of the threshold. then, coughing and spluttering in the petrol-laden fumes, he heard the door clang behind him.

the interior of a tank was not strange to derek. several times previously he had gone for joy-rides in the land-ships, but now he was experiencing a novel sensation, that of being cooped up in a mobile armoured fort in action.

there was very little room to move about. most of the interior was occupied by the powerful motors and fuel-tanks, six-pounder guns mounted en barbette, and machine-guns, to say nothing of fifteen men of the original crew. the tank was in reality a moving magazine, for, in addition to the large quantity of petrol and ammunition, she carried a stock of phosphorous-bombs, smoke-bombs, and gun-cotton. the latter explosive was for use in the event of the tank becoming disabled and in danger of falling into the hands of the enemy, and it was the duty of the last surviving member of the crew to blow the land-ship to bits should there be a danger of capture.

derek, not content to be a mere passenger, looked around for something to do. the commander of the tank was too busy to notice the new arrival. his sole attention was directed towards the enemy through the periscope sights in the roof of the mastodon.

an unattended machine-gun attracted derek's notice. a brief examination showed that the mechanism was intact. there was ammunition in plenty. a neatly-punched hole just above the sighting-aperture told its own tale. an anti-tank bullet had passed through the armour, and had hit the machine-gunner fairly in the centre of his forehead.

the tank was now lurching forward. machine-gun bullets were splaying against its nose and sides. fragments of nickel were forcing their way through the joints in the metallic beast's armour, and a sliver, cutting derek in the cheek, gave him warning that he was not properly equipped for the task.

discarding his triplex glass goggles he donned a "tin hat" and steel visor that were lying on the floor. they had been the property of the dead machine-gunner, and had he been wearing them it is just possible that the anti-tank bullet that had laid him out might have glanced from the convex surface of the steel helmet.

by this time the tank had skirted the edge of the crater and was bearing down upon a nest of hun machine-guns. even as it passed what appeared to be a pile of rubble an anti-tank gun was fired at a range of less than forty yards.

derek felt the windage of the missile as it passed completely through the armoured sides. fragments of copper and steel rattled against his visor.

bending over the sights of his machine-gun, derek prepared to deluge the concealed huns under a hail of nickel, but before he could open fire the tank made a half-turn almost in its own length and went straight for the snipers' lair.

the huns saw it coming and promptly bolted. they had but two choices: one was to hold their ground and risk being pulverized under the banded wheels of the tank; the other to risk being shot down in the open. bending low they ran. few covered more than twenty yards, for the british machine-gunners were taking a heavy toll. enfiladed by other tanks, the anti-tank gunners were completely wiped out with less compunction than if they had been rabbits in a warren.

then, swinging back into line, the tank in which derek had "signed on" as an unofficial member of the crew pressed forward towards another belt of almost intact wire, against which hundreds of demoralized boches were held up in their precipitate retreat.

on breasting the ridge the armada was greeted by a heavy fire at short range. several tanks came to an abrupt halt, burning fiercely from end to end. others, regardless of a heavy fire, held resolutely on their course, methodically flattening out obstacles and crushing boche machine-gunners out of existence.

suddenly an anti-tank bullet passed through the forepart of the tank on which derek was busily engaged with his machine-gun. the steel core passed through the head of the pilot, glanced from a metal girder, and penetrated the chest of the commander. not content with this, the deadly missile pulverized the magneto and disappeared through the floor of the tank.

promptly the huge land-fort came to a standstill. to all appearances its term of life was approaching its end. flames began to issue from one of the carburettors. in another moment the tank would have become a raging inferno but for the action of one of the drivers. grasping a "pyrene" extinguisher, he directed the oxygen-destroying chemical upon the flames. almost immediately the fire was quenched, but the noxious fumes from the extinguisher made the interior untenable. even those of the men who wore gas-masks found that these were no protection from the choking fumes, for owing to the showers of metallic splinters in the interior of the tank not a mask remained serviceable.

"out of it, lads!" spluttered the second in command, a subaltern of the tank corps. his voice trailed off into a queer little squeal of pained surprise, for a bullet, passing through a rent in the tank's side, shattered his left arm at the wrist.

quickly, yet in an orderly manner, the evacuation was carried out. the wounded men were assisted to a place of doubtful shelter afforded by an abandoned trench, while derek and the eight unscathed members of the crew followed to await developments.

even as derek crouched in the shallow trench, the greater part of which had been flattened out by tanks crossing the obstruction, he noticed an officer in the uniform of a major of the tank corps running along the irregular parados.

"back, back, all of you!" he shouted. "pass the word along. signal to the tank-commanders. we're held up, and the ground is heavily mined. retire!"