Suddenly a column of water was thrown 50ft. in the air. Stockton gave an involuntary gasp of horror—what if the submarine had fouled one of the deadly mines?
A minute passed. Even Captain Brookes began to look anxious, for no trace of the periscope was now discernible.
"There she goes again!" shouted one of the men, as another slender column rose high in the air.
Four times this was repeated, then once more came an ominous and prolonged silence. While the attention of all hands was directed towards the harbour the grey, porpoise-like hull of the submarine floundered to the surface less than a cable's length from the port bow of the Olive Branch. Thus, having announced her safe return, the little craft disappeared beneath the waves, and, guided by consummate skill and judgment, she glided underneath the hull of her parent ship.
Half an hour later her crew came on deck of the Olive Branch.
"All correct, sir," reported Lieutenant Palmer. "Every mine exploded; six in all."
"Very good," replied Captain Brookes. There were volumes of commendation in those two words, and every man who took part in the dangerous enterprise realised the fact.
"We must wait another hour till there's enough water on the bar, so our pilot informs me," continued Captain Brookes. "Mr. Sinclair, I'm going below; please report if anything unusual occurs."
"Well, old chap," exclaimed Stockton as the two friends gained the seclusion of their cabin "how did you get on?"
"Splendidly," replied Gerald, enthusiastically. "The submarine is a masterpiece. This was the mysterious object at which the captain hinted during our inspection of the wireless room. I think I've grasped the principle of it. The submarine is barely 30ft. in length and 8ft. in beam, and is housed in a cavity underneath the ship corresponding with the upper half of the submersible. Apparently its natural buoyancy keeps it adhered to the hull of the Olive Branch, but to prevent undue friction when running at full speed there are several steel doors, which, when closed, complete the normal curvature of the ship's bottom. You saw how we entered the submarine?"