Foiled in her efforts to get in touch with her consorts, U75 remained awash. The heave of the sea made it most difficult for her to use her periscope with certainty, for she had chosen a bad pitch on her ascent—the furious "overfalls" or "tide-rips" to the west of Lundy Island.
"We'll pay another visit to St. Mena's Island, Herr Rix," decided Kapitan Schwalbe, after the two officers had discussed the sinister matter of their futile attempt to make use of the wireless. "To-night at nine o'clock ought to suit. If we cannot get von Ruhle to see our signals—for my own part, I doubt whether he is in these parts—we'll have to do our best to get ashore. Meanwhile, keep a bright look-out. If we see any likely vessel coming this way, we'll try our luck once more."
"Message just received, mein herr," announced the wireless operator.
"From whom?" enquired Kapitan Schwalbe eagerly. He was devoutly hoping that either U74 or U77 had been able to "call up".
"I cannot say, sir," replied the man as he handed a code message to his superior.
Decoded, the "wireless" was as follows:
"Station 41 to unterseebooten. Two hundred gallons of fuel available here. Will be on the look-out for signals at 1 a.m."
The message was a "general call" for a secret petrol depot to any German submarine operating in the vicinity. Reference to the list of stations showed that "41" was at Port Treherne, a remote cove on the North Cornish coast about fifty miles from St. Mena's Island.
"I suppose it's safe," remarked Rix.
"With due precautions—yes," rejoined Kapitan Schwalbe. "At any rate, petrol we must have. Where's the chart? Ah, there we are! It looks a fairly easy place to approach, don't you think? The only danger from a navigation point is apparently this ledge of rocks—Lost Chance Reef, it's called. What unpleasant names these Englishmen give to their coasts!"
At that moment the Unter-leutnant, who happened to be at the conning-tower periscope, reported that a large vessel was bearing down towards them.
Kapitan Schwalbe hurried to the conning-tower. The object depicted was that of a modern tank-vessel about four hundred feet in length. She was low in the water, showing that she was well laden. In place of masts she had four stumpy poles supporting derricks. Right aft was the single funnel. The navigation bridge was well for'ard, connected with another bridge just in front of the funnel by a long slender gangway.
"An oil-tank homeward bound!" exclaimed Kapitan Schwalbe. "Just what we want to fall in with. All being well, there will be no necessity to visit either Port Treherne or St. Mena's Island. Ach! When we have taken what we require we will set fire to the ship, and the English will have a splendid view of a maritime bonfire."
The crew were ordered to their stations, the ballast tanks "blown", and U75 rose to the surface instead of "running awash", since the Kapitan had resolved to stop the tank by gun-fire.
Even then the waves were running so high that the guns' crews were almost constantly up to their knees in water.
Somewhat to the surprise of the submarine's officers and crew, the tank-steamer made no attempt to escape. The firing of a shot across her bows and the display of the black cross ensign were enough to cause the skipper to reverse her engines.
In less than five minutes, the oil-vessel was rolling in the trough of the sea and drifting slowly to leeward. Yet it was a somewhat remarkable circumstance that no attempt was made to lower the red ensign that was proudly displayed at the stern.
Kapitan Schwalbe, with his intimate knowledge of navigation, knew that the only way possible to board the prize was to run to leeward of her, and let the hull of the large vessel serve as a breakwater. He also knew that the submarine would have to be constantly under way during the boarding operations, otherwise the tank-vessel, offering considerable resistance to the wind, would drift down upon U75, whose leeway was almost unappreciable.
"Send a boat, and lower your accommodation ladder," ordered Kapitan Schwalbe, who, as the submarine ranged up half a cable's length to leeward of the tank-vessel, had left the shelter of the conning-tower and was standing on the platform in its wake.
"Aye, aye," was the prompt response.
"Board her, Herr Rix," said the Leutnant's superior officer. "Bring back her papers with you. Order them to pump heavy oil both to windward and leeward. We will then be able to run close alongside and receive her hoses."
A boat containing two seamen and an apprentice was lowered from the tank's quarter and rowed to the submarine. Into it dropped Leutnant Rix and half a dozen armed men. With them they took two incendiary bombs fitted with time-fuses.
Rix smiled grimly as he gained the oil-steamer's deck. The captain and first mate were at the head of the accommodation ladder to receive him. Most of the crew were already mustering on deck, each with a bundle containing his private effects.
"You prize to German boat," announced the Leutnant. "Make you no trouble and we you will not harm. First we will haf much oil—petroleum, is it not? Order your engineer to get steam to donkey-engine, and your men—the—the—— Hein! Ach, I haf it—the hoses to get ready. When we fill up, then twenty minutes we give you to clear out. You onderstan'?"
"Perfectly," replied the British skipper, a tall, raw-boned Scot, as he eyed the podgy German Leutnant with grim contempt. "But d'ye ken yon?"
"'D'YE KEN YON?' ASKED THE BRITISH SKIPPER, AS HE EYED THE PODGY GERMAN LEUTNANT WITH CONTEMPT"
He pointed skywards. Less than five hundred feet up, yet sufficiently far from the tank-vessel to enable the latter to screen her from the unterseeboot, was a large naval sea-plane. It was to deaden the noise of her motors that the ship's steam-pipe was continually blowing off steam from the time that U75 made her peremptory demand.
The eyes of the Leutnant and his six men followed the direction indicated by the British skipper's outstretched hand.
At that instant the sea-plane was visible above the towering sides of the British vessel.
U75 was still forging slowly ahead. In a trice Kapitan Schwalbe decided how to act. Ordering the men on deck to their diving stations, he dropped agilely into the conning-tower and gave the word for the helm to be ported.
Thus, while the quick-firers were being housed, the submarine had drawn close under the oil-tank's quarter. Here she was comparatively safe from the sea-plane, as the latter could not drop any bombs without risk of exploding the highly inflammable cargo of the British vessel.
In ten seconds the sea-plane was over and beyond her quarry. She had then to turn and circle overhead, awaiting the chance of shattering her enemy as she dived.
U75 was already disappearing beneath the waves.
She dived at a very oblique angle, steeper than she had ever done before.
Ross and Vernon, unaware of what was taking place, thought for a moment that the submarine was plunging headlong to the bed of the Bristol Channel. They had to cling desperately to the nearest object to hand to prevent themselves from sliding violently against a transverse bulkhead.
Even as they clung they heard two muffled detonations in quick succession, followed by a distinct quiver of the submarine's hull—a movement that bore a marked difference to the vibrations under the pulsations of the motors.
The sea-plane had dropped two bombs, both of which very nearly attained their object.
Kapitan Schwalbe did not bring the submarine to a horizontal position until she had reached a depth of fifteen fathoms. At that depth he was safe, both from explosives dropped from the sea-plane and also from observation. The water being still agitated, made it impossible for the observer on the biplane to follow the movements of a dark shadow fathoms deep. For once, the rough seas had been kind to U75; but the fact remained that she was still badly in want of fuel, while his last attempt had resulted in the loss of an officer and six men, who could not well be spared.