It was part of Ross's duty to report to the officer of the watch that these lamps were in order, and also, at regular intervals, that the navigation lights were burning brightly.
Presently the Sub prepared to take a cross-bearing. He was fairly certain that the Capella had reached the westernmost limit of her patrol-ground. From that point she was to proceed due south for 10 sea miles, and then due east for 20 miles until she fell in with her "opposite number".
While Barry was thus engaged, Ross noticed a sail about 2 miles distant on the starboard quarter.
"By Jove!" he muttered as he brought his glass to bear upon the stranger. "That's a funny rig."
The craft was a "two-sticker". She was square-rigged on the foremast, carrying fore-topsail and fore-course. No jibs were set; neither, as far as he could see, was any sail set on the mainmast. The vessel's sides were painted green with a broad red band.
Even as he kept the craft under observation she starboarded her helm, shaping a course that would converge upon that of the rearmost of the two tramps. By so doing she exposed a considerable portion of her broadside.
Ross gave an exclamation of astonishment. Above the green sides appeared what was undoubtedly the conning-tower and housed periscope of a submarine. "Submarine on the starboard quarter, sir!" he reported.
"What!" exclaimed Barry, levelling his telescope. "By Jove, yes! What luck!"
The unterseeboot had, of course, noticed the Capella, and had mistaken her for a trawler. She realized that she ran a risk in case the latter might be armed, but, trusting to her disguise, she hoped to get within torpedo range of the tramp—a vessel of over 3000 tons—sink her, and make her escape in the confusion that was bound to ensue. On the other hand, her Kapitan had good reasons for thinking that the supposed trawler was not one of the armed patrol, since they usually worked in company. By rigging canvas bulwarks and setting sail upon dummy masts, he was able to approach with little fear of detection.
"Action!"