From a distance of a quarter of a mile he could see the gun-crew feverishly loading their weapon, and more in the hope of delaying them than hitting anybody, he brought his nose in line and fired a series of short bursts from his machine-guns. Whether it was due to this or an order from the commander he did not know, but the men sud-denly abandoned their weapon and bundled into the conning-tower. The top closed and the U-boat began to submerge.

But by this time Biggles was over it. His bomb hurtled down. He zoomed away swiftly, banking steeply on the turn so that he could see what happened. What he saw brought a grim smile to his lips. As quick as he had been, the others were not far behind him. The Didgeree-du and the Dingo, in line, swept over the patch of swirling water. Two great columns of smoke and spray shot upwards. The stem of the U-boat rose high out of the water, the propellers racing ; higher and higher it rose until it was almost vertical ; then it plunged downwards and disappeared from sight.

For a little while Biggles continued to circle, the other machines following him, in case there should be any survivors ; but there were none, and in his heart he was relieved, for they were in no condition to take care of prisoners. A final glance at the wide patch of oil that marked the last resting-place of the U-boat and he turned back towards the islet.

Without waiting for the others to land, he raced straight on into the cave, and, jumping out, ran on to the radio room.

'Did that submarine manage to get out a signal ?' he asked Roy sharply.

'Yes, sir. It was very short though-not more than three or four words, I should say, although as they were in code I don't know what they mean. I've got a record of the letters though.'

see,' said Biggles slowly, and returned to the catwalk where the others were just corning ash.o.r.e.

'What you might call short and sweet,' remarked Algy.

'Short, but not very sweet,' answered Biggles.

Ah, well, that 's war. If it hadn't been them it would have been us. That 's what they've been handing out to unarmed ships so they could hardly complain. The Admiralty will be glad to know that one raider is out of the way. It seems to be a case where we might risk transmitting a signal. But come on, we'd better get ready for this show to-night.'

CHAPTER VI.

A DANGEROUS MISSION.

THE plan for the blowing up of the Albeck tunnel, as finally decided by Biggles and accepted without demur by the others, was completed, and as the weather remained favourable it was agreed to put it into operation that night. Two machines would go over, the first to be the Willie-Willie converted into a two-seater, with Biggles and Ginger in it. This was actually the operative aircraft. It would carry the explosive charge-a time bomb-with which they hoped to destroy the tunnel, and fly at its maximum ceiling, which Biggles thought could not be less than 25,000 feet. This would, of course, involve the use of oxygen apparatus, which had not been overlooked by the Admiralty in fitting out the base. Algy, in the Didgeree-du, also converted into a two-seater, was to take off twenty minutes after the others and fly at 10,000 feet with a dual role to play. Primarily, his purpose was to act as a decoy to distract attention from the operative machine by drowning the noise of its engine with its own. Secondly, it could act as a reserve plane to pick up the occupants of the first machine if by any chance it should be damaged in landing. If its services were required Biggles would signal to it by means of a red light ; otherwise, it was to return home independently.

Biggles saw clearly that the greatest difficulty to be overcome was to reach the landing-field un-detected, for it was too far inland to be reached in a glide after the manner adopted in the attack on the ammunition dump. He knew that if once the machine was picked up by the ever-questing searchlights it would not only be futile to land, but suicidal ; so, after giving the matter consider-able thought, he had decided on the scheme just outlined as the most likely way of escaping obser-vation. Algy was to fly straight towards the land-ing-field, drawing both the searchlights and the anti-aircraft gunfire. In this way it was hoped that the other machine, flying 15,000 feet above it, would, by cutting its engine some distance away, be able to reach the field more or less silently.

Once the Willie-Willie was on the ground matters would have to take their course.

Biggles would have to open his engine in order to get off again, but this he did not mind, trusting to his ability to get back in the face of anything the enemy might do to prevent it.

To start with, the watches of both machines would be synchronized; both aircraft were to rendezvous over the islet at a prearranged time, at their respective alt.i.tudes, and fly on the same com-pa.s.s course at the same speed. This should (as Biggles explained) keep them together, for they would not be able to see each other. He, having to climb to a greater height, would take off first. The scheme was not entirely satisfactory, but he was convinced that it was the best they could do in the circ.u.mstances.

'We'll start as soon as it 's dark,' he concluded. 'It may take us some time to get into the tunnel, and it wouldn't do to be caught out in daylight.'

Accordingly, the machines were made ready, and at nine p.m. the Willie-Willie, with Biggles in the pilot's seat and Ginger crouching over a gun behind him, taxied out to the cove. Another minute and they were in the air, spiralling steadily upwards.

For twenty minutes the steel airscrew of the Willie-Willie clawed its way into the starlit heavens, by which time the altimeter needle registered 22,000 feet, and the airmen adjusted their oxygen apparatus ; then, still climbing slightly, Biggles struck off to the south-west at a steady speed of 28o miles an hour. Half an hour later the German mainland appeared ahead, black, sinister, as mysterious as another world. A finger of gleaming silver stabbed the darkness, and soon the air was cut into sections by the ever-alert searchlights.

Biggles's voice reached Ginger over the tele-phone. 'Look down,' he said. 'Poor old Algy seems to be copping it.'

Ginger looked over the side. Far below, so far that they appeared to be on the ground, a hundred flickering points of light danced in the darkness, and he knew it was the archie barrage throwing a curtain of fire round Algy's machine. It was hard to believe that the bursting sh.e.l.ls were 0,000 feet above the earth. For a time he watched the barrage moving along below them, and from it was able to judge roughly the position of the Didgeree-du. Algy was getting the worst of it now, he reflected, but their turn would come later.

Once a probing beam swept perilously close to the Willie-Willie, but Biggles side-slipped away, sacrificing a little height in the slip, but keeping on his course.

The minutes pa.s.sed ; one by one the searchlights went out and the barrage thinned, as the coastal batteries were left behind. Below, the earth was wrapped in profound darkness, but the roads showed dimly, like pale threads snaking across the vast panorama. Woods and forests showed as inky stains on the vague background of the earth. Occasional flashes still followed the course of Algy's machine, and the cunning of Biggles's plan became apparent, for so far not a single sh.e.l.l had come near the Willie-Willie, and it seemed fairly certain that its presence had not been suspected by the watchers on the ground. Shortly afterwards the archie trail swung away to the left, and Ginger knew that Algy had begun to circle away in accordance with their plan. That Biggles had noticed it, too, was made apparent when the Willie-Willie's engine died, leaving the machine to glide silently along its lonely course.

Standing up to look immediately below them, Ginger saw what he expected to find-the railway ; a long straight line that began in the indistinct distance behind them and vanished into the black horizon ahead. He considered it seriously, know-ing that Biggles'

s skill in pilotage would now be severely tested, for to bring a machine down from such a height on a given landing-ground, at night, without touching the throttle, required more skill than the average pilot possessed.

Once a curious, nebulous ball of fire rolled along the line, and he knew that it must be a train ; the lights in the carriages were out, but the fireman could not prevent the glow from reflecting on the smoke as he stoked his furnace.

Ginger thought the glide would never end. It seemed interminable, the more so because, owing to their great height, they did not appear to be moving ; nor did they seem to get any lower, although he knew that this was not the case, for the altimeter told a true story and the needle was swing-ing back all the time.

Staring fixedly ahead, he saw the thin line of the railway end abruptly, as if it were cut off short in open country, and he knew they had at last reached the tunnel. A moment later the machine began a wide, flat spiral, and the details on the ground soon showed up more clearly. The moon had risen, and in its cold blue light he could even see the farm-building at the northern end of the tunnel which he knew must be the guard-house.

Quickly now the greys became less dim, and the outlines of woods and hedges stood out more sharply. A wide river, which he knew must be the Elbe, meandered across a deserted landscape to the north-west, for villages were few and far between.

A current of air on his left cheek interrupted his survey as the machine went into a steep side-slip, and he realized that Biggles must have arrived over the objective with plenty of height to spare ; he noted it with satisfaction, for had they undershot they could only have reached the landing-ground by opening the engine. Looking ahead he could see it, a large field roughly triangular in shape, with a group of trees at the apex. He glanced at Biggles, and saw that he was leaning forward as he operated the gear that lowered the undercarriage wheels.

The field was under them now. Almost imper-ceptibly the nose of the machine came up as Biggles flattened out. The tail sank a little, but still the machine glided on towards the trees, its wheels about two feet above the gra.s.s.

Ginger held his breath and waited, praying that there were no unseen obstacles, for on the floor of his c.o.c.kpit rested a small, square wooden case con-taining enough high explosive to blow the machine to atoms. He breathed again as the wheels touched, b.u.mped gently once or twice, and trundled on to-wards the trees. He felt the machine strain slightly as the left wheel brake was applied, causing the air-craft to swing slightly so that it finished its run a dozen yards from the trees, facing the open field ready for an instant take-off should danger threaten. Silence fell.

'Well, here we are,' remarked Biggles quietly.

'Nice work, chief,' acknowledged Ginger.

They both got out of the machine, Ginger taking the explosive charge with him, and stood still, listening, peering with straining eyes into the dim moonlight, for there was just sufficient light for it to be deceptive.

'Everything seems to be quiet ; I don't think we were spotted,' said Biggles at last. 'Give me a hand.'

Slowly, and not without effort, they dragged the machine back into the dense gloom under the trees, leaving it with its nose still pointing to the open field. There was no movement of air, so the question of the direction of the wind did not arise.

'Good! She'll do nicely there. We'll get along,'

muttered Biggles softly, and picking up the time-bomb, set off down a hedge that led in the direction of the tunnel.

They came to a gap, and crawling through it, came out in a lane, which they followed for some distance ; then Biggles cut across country, keeping as close as possible to the hedges, until they came to a slight embankment. 'We're about over the tunnel,' whispered Biggles. 'If we turn right here it should bring us to the entrance.'

In a quarter of an hour, now moving slowly and with infinite caution, they came within sight of the railway line. Lying flat, Biggles surveyed the scene. There was no one in sight. The guard-house, a square black barn, stood about a hundred yards away, but of the sentries there was no sign. He crept forward for a short distance and again lay still, straining his eyes to find the men who he knew must be there.

He was still staring into the tricky half-light when the door of the barn was suddenly thrown open ; a shaft of yellow light fell athwart the gra.s.s, and a peremptory voice, in German, called, 'Keep your eyes open there ; there 's been an air-raid warning.'

'Jawohl,' was grunted in answer, so close to where he lay that Biggles instinctively stiffened.

The door was closed and the light disappeared. Silence returned. But it did not last long. '

Did you hear that, Fritz ?' said the voice that had last spoken.

'Ja,' came the reply, heavy with boredom, some distance away. 'Anybody would think that the Englanders were coming here. The corporal 's nervous. He ought to go into the trenches for a bit ; that'd cure him.'

Biggles smiled grimly and felt for Ginger. shall have to knock this fellow on the skull,' he breathed. 'If he makes one sound we're sunk. Keep close to me.' He drew his revolver, and hold-ing it by the barrel, began to creep forward. He had not far to go. A round forage-cap appeared silhouetted against the sky. Beside it, at an angle, was the black outline of a bayonet.

For several minutes Biggles lay still, trying to work out the best way of approach, for there seemed to be a low growth of brambles between him and the sentry, and to cross these without making a sound was manifestly impossible. He was still lying there when, from far away, came the drone of an aero-engine, its steady purr punctuated by the dull whoof, whoof , whoof, of archie. He knew that it was Algy, still cruising about watching for a possible signal.

'h.e.l.lo, Fritz, here comes the Englander,' called the sentry excitedly. 'Come here, you'll see better.'

The last word died on the man's lips, for know- ing that if the two sentries came together his task would be infinitely more difficult, Biggles had risked all on a desperate chance. The sound of the man's voice deadened the slight crunch of briars as Biggles crept swiftly across them, added to which the sentry's interest was entirely absorbed by the approaching aircraft. He was staring up into the sky when Biggles rose like a black shadow behind him and brought the b.u.t.t of his revolver down on his head. The man dropped without a sound.

Tight lipped with anxiety, Biggles whipped off the man's cap and put it on his own head.

s.n.a.t.c.h-ing up the rifle, with the bayonet fixed, he rose erect just as the second sentry came over the brow of the slope not half a dozen paces away.

Ah, there you are,' grunted the German as he came on. 'What are you doing ?'

Biggles dropped the point of the bayonet until it was a foot from the man's breast. 'One sound and you die,' he said sharply in German, and there was a vibrant quality in his voice that confirmed his dire threat. 'Drop your rifle,' he added.

After his first gasp of astonishment the man made no sound. The rifle fell to the ground with a thud.

'Now lie down on your face and you will not be hurt,' commanded Biggles.

The man obeyed.

'Ginger, pull his greatcoat over his head and tie [image]

it round his neck with the belt,' went on Biggles. 'Now tie his wrists behind his back with your handkerchief-pull it tight.' He opened the flap in the b.u.t.t of the rifle and took out the cord pull-through used for cleaning the barrel of the weapon. Kneeling, he wound it twice round the sentry's ankles and knotted it.

Now these operations had taken perhaps two minutes, and all the time the aeroplane had been drawing nearer. And that was not all. The door of the barn had been thrown open, and half a dozen men poured out, talking excitedly, staring up at the sky. A telephone bell jangled. As if this were not enough, the rumble of a train could be heard approaching the southern end of the tunnel.

Biggles s.n.a.t.c.hed up the time-bomb. 'If either of these fellows moves. .h.i.t him on the head, ' he said grimly. 'If those guards come this way, leave me ; make for the machine and save yourself.' Before Ginger could answer he had scrambled down the slope and disappeared into the tunnel.

With his heart beating painfully from suppressed excitement, Ginger squatted beside the sentries, watching the men outside the barn, for in them lay the greatest danger. Once one of them shouted something, presumably to the sentries, but as Ginger could not speak German he did not know what was said, and could only remain silent. Over-head, the aircraft was now turning for home.

Ginger waited. A minute pa.s.sed; it seemed an eternity of time. Another minute went by.

What on earth was Biggles doing, he wondered feverishly ? If he wasn't quick he would be knocked down by the train. Then, to add to his panic, one of the men outside the barn detached himself from the group and hurried down the line towards him.

Ginger drew his revolver and curled his finger round the trigger. Why didn't Biggles come ?

The man gave a shout and broke into a sprint, and the next instant the reason revealed itself. Biggles came panting up the embankment. 'Run for it,' he gasped.

The man on the line shouted again. It was answered by others. A shot rang out.

'Keep going,' panted Biggles, as they tore through the brambles and made for the hedge that led in the direction of the landing-ground.

Ginger, s.n.a.t.c.hing a glance over his shoulder, saw a line of figures on the top of the embankment, but the next second he was flung flat on his face as the ground rocked to the roar of an explosion that nearly burst his eardrums. Dazed, he staggered to his feet.

Biggles caught him by the arm. 'Keep going,' he said again.

If there was a pursuit Ginger saw no more signs of it. His knees were weak under him by the time they reached the field in which the plane had been left. Gasping for breath, for they had crossed a ploughed field and their boots were caked with mud, he staggered on. Biggles, too, was puffed, and had to slow down. The group of trees that concealed the machine was still some distance away, but they plodded on, keeping close to the hedge. Once an aeroplane, its navigation lights ablaze, roared over them.

'They've got fighters up, looking for Algy I suppose,' panted Biggles. 'They'll be after us, too, presently,' he added, as they reached the machine, still standing as they had left it.

'Have we got navigation lights on ?' asked Ginger suddenly. 'I forgot to look.'

'Yes-why ?'

'Then why not switch 'em on and fly low ?' Biggles stared. 'Have you gone crazy ?'

'I shouldn't be surprised, but I was thinking that they would take us for one of themselves and leave us alone.'

Biggles laughed aloud as he scrambled into his seat. 'Brilliant idea,' he declared. 'We can always switch the lights off if the dodge doesn't work. Come on-let's go.'

Ginger climbed into his seat ; the machine raced across the dew-soaked turf and in a few moments was in the air, heading northward.

As soon as they were at a thousand feet Biggles switched on the navigation lights, clearly revealing their position to anyone on the ground. He was only just in time, for a searchlight beam was already feeling its way towards them ; but as the lights came on it swung away so as not to dazzle (as the operator evidently thought) the pilot of one of his own machines.

Ginger chuckled. The scheme was working. In-deed, it worked far better than they could have hoped, for not once were they challenged either by searchlights or anti-aircraft guns. They had one shock, and that was when an enemy machine, also carrying lights, came close to them, and actually flew for a short distance beside them. But appa-rently the deception was not suspected by the pilot of the German plane, for presently it turned away and disappeared into the night.

As they crossed the coast-line Ginger let out a yell of triumph. Biggles did not answer, and lean-ing forward to see why, Ginger saw him staring ahead with a tense expression on his face, revealed in the luminous glow of the instruments. 'What 's wrong ?' he cried.

Biggles's answer was terse.

may be wrong, but that looks like fog ahead.'

Hardly had the words left his lips when a wisp of clammy moisture clutched at the machine, and the next instant everything was blotted out.

With his eyes on his instruments, Biggles switched off the navigation lights, which could no longer serve them, and easing the stick back, started to climb. He knew that it was no use trying to get under the fog, for he was already flying so low that to fly lower would be dangerous. There was just a chance, however, that if the fog proved to be no more than ground mist he might be able to get above it and see through it ; for it is a curious fact that what at a low alt.i.tude may be an opaque blanket, can become transparent from a great height. But when the Willie-Willie had climbed to 5,000 feet, and was still fogbound, he knew that height would not help them ; still he went on climb-ing, and shortly afterwards emerged into a cold, tranquil world of utter loneliness, beautiful in a way, but almost terrifying in its desolation. Overhead, the moon and stars gleamed in the dark blue vault of heaven, throwing a silvery sheen on the ocean of cloud that lay below, an expanse as flat as an Arctic snowfield, stretching as far as the eye could see. Just above it roared the Willie-Willie, with its shadow, surrounded by a misty halo, keep-ing it company.

With his eyes on the compa.s.s Biggles flew on. Half an hour pa.s.sed and he knew that they must be somewhere near their base, but no break appeared in the all-concealing blanket that lay below. He dare not go down now for fear of colliding with the rock, so he started to circle, hoping to find a break in the fogbank ; but it was in vain.

Two courses now lay open to him. Either he could turn away from the base, and, flying by instruments, endeavour to put the Willie-Willie down on the open sea, or he could continue circling in the hope that the fog would disperse before his petrol ran out. This, however, was unlikely, for he had only an hour's petrol left, and he knew from experience that the fog would probably persist until it was banished by the rising sun. If the fog did not disperse, then in an hour he would have to go down anyway, so he decided to go down while there was still petrol in his tanks ; otherwise, even if he did get down safely, he would find himself adrift on hostile waters.

The steady roar of the engine died away as he cut the throttle and raised the landing wheels that would not again be needed ; at the same time he pushed the joystick forward.

With the air hum-ming a mournful dirge through the slowly rotating propeller, the machine glided down to the silvery plain that seemed to stretch to eternity, as smooth and level as a frozen sea. For a few seconds the floats ploughed into it, tearing it up like cotton wool ; then the fog took the machine into its clammy grip.

Biggles sat quite still, his eyes on the altimeter needle. Minutes pa.s.sed, minutes as long as hours, while the needle crept back round the dial-4,000 . . . 3,000 . . . 2,000 . . . 1,000.

Still the gloom per-sisted. The acid test was now to begin. The needle continued its backward revolution, quivering slightly, over the hundred-feet mark.

Biggles had this advantage. He was not landing on unknown country where there was a risk of colliding with a hill, a high building, or trees. He had set the altimeter at sea-level, and to sea-level they were returning. He could, therefore, fly to fine limits.

Inexorably the needle sank, ticking off the hundred marks on the dial. Biggles had pushed up his goggles and was leaning over the side of the c.o.c.kpit, blinking the moisture off his eyelashes as he stared down into the void. Two hundred feet, and there was still no sign of the black water which he knew was there ; a hundred. . . .

Ginger held his breath and braced himself for the shock which he felt was inevitable. The altimeter needle came to rest on the pin. Zero I Simultaneously a dark indistinct ma.s.s loomed up below.

The machine flattened out as Biggles s.n.a.t.c.hed the stick back and held it level. The dark ma.s.s disappeared, returned, and then showed as black as ink. Biggles pulled the stick right back into his stomach. The Willie-Willie lurched sickeningly, and then sank bodily.

Splash! A cloud of spray rose into the air. For half a minute the machine forged on, drenching itself with water. Then it came to rest. Biggles flicked off the ignition switch; the propeller stopped its rhythmic ticking. Silence fell. Silence utter and complete.