Ginger, gliding at 5,000 feet towards the scene of action, had seen all that Biggles had seen. In fact, he had seen, more, for so far he was un-molested, and flying on a straight course towards the ca.n.a.l, was able to get a clear view of it. From a distance he had seen Biggles's bombs explode, and, shortly afterwards, the destruction of the end shed. He had watched the archie barrage follow-ing him, and then return with renewed violence to the area in which Algy in the Didgeree-Du was now taking up the fight. He saw, too, the explosion of Algy's bombs, although by this time he himself was preparing for action.

The wisdom of Biggles's plan was now. apparent, for not only was he down to a thousand feet, but he had been able to line his machine up with the sheds, which he could see clearly in the lurid glow of the fires, without his presence being suspected.

This satisfactory state of affairs, however, was not to last. Trembling a little with excitement in spite of his efforts to remain calm, he had com-menced a shallow dive towards the objective when a searchlight suddenly swung round and flashed on his wings. It overshot him, and before it could turn back he had steepened his dive so that it sought him in vain. Nevertheless, the damage had been done, and in a twinkling the other lights were probing the air around him.

His mouth turned dry as the first archie sh.e.l.ls lacerated the air dangerously close to him. He knew they were close because he could hear the m.u.f.fled explosions above the roar of his engine, and Biggles had told him that archie was only dangerous when close enough to be heard. He had expected the barrage to be bad, but not quite as terrifying as this. Several times he felt splinters strike the Dingo, and although he tried hard not to think about it, his imagination refused to be side-tracked so easily. However, he kept his eyes on the sheds, determined to get a direct hit or die in the attempt. To endure all this danger for nothing was not, he thought, to be borne. Once he caught a glimpse in his reflector of the inferno that raged in the sky behind him, and the muscles of his face went stiff. Still, he reasoned, Biggles had gone through it ; so had Algy ; therefore, so must he.

An unseen missile crashed through the machine just in front of him with terrifying force.

Some-thing struck him on the cheek with the bite of a whiplash, and he grunted with pain. Putting his hand to the place, he stared fascinated by the sight of his own blood.

Reaction came swift and strong ; and, as so often happens, it took the form, not of fear, but of bitter resentment, and he looked for the target with a personal interest. T11 show you,' he muttered furiously, and jammed the stick for-ward in a kind of fierce exultation.

Down-down-down, he roared, careless now of the storm of fire that raged about him. '

I'm going to get those sheds or bust,' he told himself desperately, and it was no idle boast.

A glance at the altimeter gave him a shock, for the needle was nearly on zero ; he had not realized that he was so low.

In a sort of daze, feeling that the thing was not really happening and that he would presently wake up, he took aim with calculated deliberation. He was still a little short of the target, and the second or two that he had to wait exasperated his patience. He wanted to see the bomb burst and blow every-thing sky high.

Slowly, as the wing crept up to the first shed, his hand groped for the bomb-toggle. '

Now,' he muttered, suddenly conscious of a sense of power, and pulled the handle back as far as it would go. The Dingo b.u.mped as the steel-clad load of high explosive plunged earthward.

Ginger was torn between a desire to wait and watch what happened and an urge to dive clear ; fortunately for him his common sense prevailed, or it is unlikely that he would have lived long enough to know how successful he had been. He had zigzagged away as Biggles had told him, and was about to turn to see the result of his effort when the entire world seemed to blow up, lighting earth and sky in one terrific blaze. He felt the heat of it on his face. The Dingo, caught in that fearful blast, soared dizzily, throwing him against the safety-belt with a force that made him gasp. Tem-porarily blinded and half stunned by shock, he skidded crazily round the sky not knowing which way to go. In a subconscious way he noticed that most of the searchlights had gone out ; nor was the archie as bad as it had been. The lattice mast of a wireless tower seemed to leap out of the darkness towards him, and he dragged the stick back into his thigh in a panic. He missed the mast by inches, but the shock did something to restore his senses to normal. '

Gosh! I'm nearly on the ground,' he thought frantically, and made haste to correct the error. He saw the ca.n.a.l, and made for it like a pigeon ; for a few seconds he followed it ; then , happening to glance at his compa.s.s, he saw that he was going the wrong way.

Again it was in something like a panic that he whirled the machine round and sped like a bullet towards the open sea. For some minutes the archie followed him, but in some curious way he had ceased to be alarmed by it. He began to laugh, but pulled himself up abruptly. 'That won't do,' he told himself seriously, and remembering the wound in his face, he felt it carefully. It was still bleeding, but, as far as he could make out, not badly.

In any case, he was not conscious of any pain, so he thought no more about it. He did not bother to climb for height, but checking his compa.s.s, set about getting home by the shortest possible route. He remembered Biggles and Algy, and wondered vaguely how they had fared, but his thoughts were chaotic and he found it difficult to concentrate.

suppose I shall get used to this sort of thing,' he mused philosophically.

He could see the black bulk of Bergen Ait some time before he reached it ; indeed, he was surprised that he could see it so plainly. He scanned the sea for ships, but there was none in sight, for which he was thankful, for it permitted him to make straight for the cove.

It was clear when he reached it, but as he glided down he could just make out one of the other machines being towed into the cave. Three flashes of a green light gave him the signal to land, and in a minute or two he was on the water, taxi-ing to-wards where he knew the entrance of the cave to be. The Dingo seemed strangely sluggish, but he thought nothing of it until the motor-boat dashed out, with Briny in the bows making frantic signals to him to hasten. Obediently he gave the engine more throttle, and roared into the cave, where the motor-boat took the machine in tow and dragged it to the catwalk.

He switched off and pushed up his goggles. 'What 's the matter ?' he asked weakly.

Biggles answered. 'You were sinking. You must have got a float holed. It's all right now; the Flight-Sergeant will attend to it.'

Ginger sprang up in alarm. 'Great Scott!' he cried, didn't know.'

Biggles helped him ash.o.r.e. 'Good work, laddie,' he said patting him on the back ; 'you got it a beauty.'

'How did you know ?' inquired Ginger. 'Did you see it ?'

certainly did-that is, I saw the blaze on the sky. They saw it from here-and heard it.'

Ginger stared. 'Well, do you know, that's a funny thing,' he said shakily ; was right on top of it yet I didn't hear a blessed thing.' He staggered suddenly.

Biggles caught him. 'Bear a hand, Algy,' he said sharply, noting the blood on Ginger's face. He's been hit. He needs medical attention.'

Ginger laughed foolishly. 'Don't you believe it,' he protested ; 'what I want is my supper.'

CHAPTER V.

AN UNWELCOME VISITOR.

FOR three days the Boomerang Squadron had no further instructions from London, for which Biggles was grateful, for the respite gave him time to organize things at the base to his entire satisfac-tion, and gave Ginger's face a chance to heal. The wound turned out to be a very slight one, no more than a cut from a flying splinter. Even so, in his excited condition it was enough to give him a temperature, and much to his disgust Biggles ordered him to remain in bed for a day. The period of inactivity also gave the Flight-Sergeant an opportunity of repairing the machines, all of which had been more or less damaged by gunfire.

Only one signal was received, and this could not have been more brief. It consisted of a single word, 'Congratulations'.

'I suppose that 's from Colonel Raymond,' said Ginger. 'How do you suppose he knows how much damage we did-when we don't really know our-selves ?'

Biggles laughed shortly. 'He knows all right, you can bet your boots on that,' he a.s.serted.

'We've got agents on the spot, I'll warrant. Some-body told me that we had an agent at Kiel right through the last war. Anyway, since Headquarters has gone to the trouble of congratulating us, we must have made a nasty mess of the dump.'

One other item of news interested them im-mensely, and this they received on the ordinary radio, a powerful instrument on which they could get all the world's programmes. They rarely had time to listen to music, but the news broadcasts kept them up to date on the progress of the war. The item that pleased them most was the story of the raid by R.A.F. Squadrons on the German battleships at the entrance to the Kiel Ca.n.a.l.

It had occurred on the same day as their own raid, and Biggles realized that the two raids must have been part of the same plan to destroy the enemy's equip-ment in the ca.n.a.l zone.

It was late in the morning of the third day after the raid that the next signal was received.

The three pilots were sitting in the tiny mess, listening to Briny, who was describing with a wealth of graphic detail a raid in which he had once taken part against the cannibals of the Solomon Islands.

'Ten thousand of 'em there was, all as black as midnight, a-dancin' and brandishin' their spears ; and only me and my old shipmate Charlie to face 'em,' he declared in a hoa.r.s.e whisper. "Charlie," I sez, "you attack 'em in the flank. I'll tackle 'em in front. Charge!" I yells, and you wouldn't believe it 'You're quite right, Briny, I wouldn't,' put in Biggles sadly. 'Personally I could charge a well- ,.

done steak right now, so Roy hurried into the room with the signal. He saluted and handed it to Biggles who, after a glance at the coded message, took it to the records room, the others following. He unlocked the safe, took out the code-book, and the envelope to which the signal referred.

'They seem to have got our jobs all ready for us before we came,' remarked Algy.

'The Colonel as good as told us so,' reminded Biggles. 'It was only to be expected. Our people have got spies on the mainland, and probably knew before the war started the most vital objectives which could be reached by a unit stationed here.' He read the orders in silence, the others watching his face anxiously.

'Well ?' exclaimed Algy at last, impatiently.

Biggles glanced up. 'Listen to this,' he said quietly. "To Officer Commanding Z Squadron, on detached duty. On the first night after receipt of these instructions on which weather conditions are suitable, you will destroy the tunnel on the Berlin- Hamburg railway at Albeck, about sixty miles from the coast, as shown on the enclosed map. Owing to the depth of the tunnel it is not possible to do this by direct bombing. The only way success can definitely be a.s.sured is by placing an explosive charge (case W.D.

6. in your stores) in the tunnel. This will involve landing in enemy territory. A suitable field, one and a quarter miles from the tunnel, is marked in red on the map. You are warned that both ends of the tunnel are guarded day and night by double sentries. The guard-houses are situated as follows. At the northern end, a farm building seventy-eight yards north-east.

At the southern end, a signal box twenty-five yards south-south-east. Receipt of these instructions will be acknowledged by a double A transmitted on the wave-length allotted to you three times at intervals of three seconds."

Biggles finished reading, laid the paper on the desk and tapped a cigarette reflectively on the back of his hand.

'Very pretty,' announced Algy cynically. 'Do they think we possess some means of making our-selves invisible ?'

'That 's all right, old boy, you needn't come,' murmured Biggles casually.

Algy started forward belligerently. 'What do you mean-I needn't come ? You can't leave me out of a show like this-'

'I'm sorry,' broke in Biggles blandly, 'but I rather gathered from your remark that you'd prefer to stay at home.'

'Well, think again,' snorted Algy.

'And that's no way to talk to your commanding officer,' returned Biggles. 'All right. We'

ll tell Roy to send the acknowledgement and then, with the map in front of us, think of ways and means. As a matter of fact, I did a job like this once before,' he added, as they went to the radio room and gave Roy instructions concerning acknowledgement of the orders.

Roy, with earphones clamped on his head, made a note on his pad. 'By the way, sir, I'm picking up a lot of Morse,' he said. 'I think it 's being sent out from somewhere not very far away. It 's in code, of course.'

'By jingo, if we could read it, it would be useful!' exclaimed Ginger. 'Do you think we could decode it ?'

'Not a hope,' answered Biggles promptly. 'What point would there be in using a code that could be deciphered by the enemy ? The only way official messages can be deciphered in war-time is with the official key, and that 's something we're not likely to get hold of. I imagine the British government would be only too pleased to pay a million pounds for the German secret code at this moment. All the same, Roy, you can keep a record of any Morse you pick up-one never knows. Get that acknow-ledgement off right away.'

'Very good, sir.'

Biggles led the way back to the office and spread the map on the table. 'All we can do is memorize the spot,' he said, pointing with his forefinger, 'and work out the best way of getting to it. We shan't need three machines; two should be enough, one to do the job and the other to act as a reserve-and possibly a decoy. I'll think about that. If the weather is O.K. we may as well go to-night and get it over. Algy, go and dig out that box marked W.D. 6. I'll go and have a look at the sky. No,' he added as an afterthought, 'there 's no need for me to go. You go, Ginger, while I have a look at the map.'

Leaving Biggles pondering over the map, Ginger made his way along the catwalk. He stopped for a few minutes to speak to the Flight-Sergeant, who was still working on the Dingo, and then went on towards the mouth of the cave.

Even before he pulled the tarpaulin aside he was aware, from the shrill cries of the gulls, that some-thing unusual was happening outside. Thinking that possibly the cause was a coming change in the weather, for he knew that gulls often get excited at such times, he m0ved the heavy tarpaulin and looked out. Instinctively his eyes turned upwards to the birds. Normally the majority sat placidly on the ledges on the face of the cliff, but now they all appeared to be on the wing, and he was amazed at the number of them. The air was full of whirling white forms, thousands of them, wheeling and at the same time uttering discordant cries of alarm.

At first Ginger could see nothing on account of the birds, but as he stared he became aware that they seemed to be concentrating at two places, not very far apart. Focusing his eyes on the spot, he caught his breath sharply as he perceived the reason for the uproar. Two men in dark uniforms were creeping along a ledge ; in their ha.nds they carried baskets in which they were putting something which they were picking up from the rocks.

It did not take Ginger long to realize that they were collecting the eggs of the gulls, which were protesting at the outrage in the manner already described. For a full minute he stared at the two men as his brain strove to grasp the significance of their presence.

Unprepared for anything of the sort, he was for the moment completely taken aback ; but as his composure returned he realized that a boat of some sort must have brought them, and he looked along the foot of the cliffs to locate it. It was not hard to find. It was a small collapsible canoe. Sitting beside it, calmly- smoking a pipe, was a third man.

Again Ginger's eyes moved, for he knew that such a frail craft could not have made its way to the rock across the open sea, and what he saw turned him stiff with shock. Lying just off the entrance to the cove, not two hundred yards away, was a sub-marine, its grey conning-tower rising like a monu-ment above the deck. There was no need to question its nationality, for on the side of the tower was painted, in white, the single letter U. Below it was the number 159.

How long the submarine had been there, Ginger, of course, did not know, but it had evidently been there for some time, for several members of the crew were disposed about the deck, sunning them-selves in the autumn sunshine, while a line of washing hung between the conning-tower and a circular gun turret.

Ginger was still staring, half stunned by shock, when he heard a noise inside the cave that galvan-ized him into frantic activity. It was the swish-swish of an engine as its propeller was turned preparatory to starting, and he knew that Smyth was about to test the Dingo. Releasing the tarpaulin which he was still holding, he tore back along the catwalk and nearly knocked the Flight-Sergeant into the water with the violence of his approach. He was just in time, for the Flight-Sergeant's hand was already on the starter.

'Stop !' he gasped. 'Don't make a sound.' Leav-ing the mechanic gazing after him, as if he had lost his reason, he dashed along to the records room, where he found Biggles and Algy still poring over the map.

Their eyes opened wide at the expression on his face. 'What 's wrong ?' snapped Biggles.

Ginger pointed down the cave. 'There 's a U-boat in the cove,' he panted.

There was dead silence for a moment. Then Biggles sprang to his feet. 'The d.i.c.kens there is,' he said tersely. 'What's it doing ?'

Briefly, Ginger described the situation.

'I'd better have a look,' muttered Biggles. 'There seems to be nothing we can do except sit quiet in the hope that it will soon clear off.'

'Suppose these bird-nesters find the cave ?' asked Ginger.

'It'll be the last birds'-nesting they do for a long time,' promised Biggles grimly.

'It's the U 159,' Ginger informed him.

Biggles clenched his fists. 'By thunder,' he swore, 'here's a chance. It was the U 159 that sank the liner Arthurnia without warning, so it would be just retribution if we handed it a basinful of the same medicine. It must be on its way back to its depot. Come on.'

He dashed off down the catwalk closely followed by the others, but nearing the tarpaulin he slowed down and peered cautiously round the end of it.

The U-boat was still in the same positi0n, but the men who had been ash.o.r.e, evidently having filled their baskets, were making their way back in the canoe. Reaching the submarine, they climbed leisurely on board.

'They seem to be in no hurry,' observed Biggles anxiously. 'I'm afraid we're going to have them hanging about for some time. Ginger, send the Flight-Sergeant to me.'

Presently the Flight-Sergeant came at the double, and Biggles gave him orders in a low voice. 'Get an armour-piercing bomb on each machine and cast off ready for instant action.' He turned to the others. 'If she finds the cave we shall have to go for her,' he explained. 'There are probably forty or fifty men on board, so if they once got ash.o.r.e we shouldn't have a chance. They'd radio our position to Germany, anyway, and probably plaster us with that heavy gun on the bows. Our machine-guns wouldn't be much use against that. I'm still hoping they'll go without finding us.'

An hour pa.s.sed, and still the submarine gave no indication of departure. Another hour went by ; the washing was taken in and the deck cleared, but not until mid-afternoon did the sinister craft begin to turn slowly towards the open sea.

Biggles breathed a sigh of relief. 'She 's going,' he said. 'That 's the best thing that could happen for everybody.'

With her steel deck awash, the submarine ploughed its way slowly towards the south, the air-men watching it with mixed feelings of relief and regret, for such a mark might never again present itself.

Ginger, who had fetched a pair of binoculars, steadied himself against the rock and brought them into focus. 'How far is it away do you think ?' he asked Biggles.

'About a couple of miles-why ?'

'It 's stopped-at least, I think so. Yes, it has,' declared Ginger. 'There seem to be some officers on deck-they're looking at something on the water. By gosh 1 It 's coming back.'

Biggles grabbed the gla.s.ses-not that they were really necessary, for what Ginger had said was obviously correct. The submarine had swung round in a wide circle and was returning over its course.

'What's the idea ?' asked Algy. 'What could they have seen to bring them back ?'

Biggles snapped his fingers. 'I've got it,' he cried. 'Look!' He pointed at an iridescent stain that drifted from the mouth of the cave and spread in a long wavy line towards the southern horizon. 'They've spotted that oil,' he added sharply. 'They're on their way back to see where it's coming from. It'll bring them straight to the cave. Quick! The machines!

We've got to get that sub. or it 's all up with us. Pull that tarpaulin out of the way, Smyth.'

There was a rush for the machines. Biggles was away first, as he was bound to be, for the Willie-Willie was nearest the entrance and blocked the way of the others. The roar of its engine drowned all other sounds. Leaving a wake of churning water behind it, the machine shot through the entrance to the cave and raced on over the cove.

It b.u.mped once or twice as it struck the swell of the open sea, and then, after climbing for a moment or two at a steep angle, made straight for the U-boat.

Biggles knew that there was no time for tactics. In the first place the members of the submarine crew must have heard his engine start, and no doubt they could now see him.

That was not all. He knew that he had got to send the U-boat to the bottom before a wireless message could be sent to the sh.o.r.e, or a flotilla of destroyers would be round the islet like a pack of wolves round a wounded deer. It was in an attempt to prevent this happen-ing that Biggles roared straight at the submarine.