Just before sundown the Portchester Castle was, roughly, twenty miles east of Gibraltar. It was a calm, glorious evening. Not a ripple disturbed the placid surface of the Mediterranean, save the long, ever-diverging swell in the wake of the slowly moving vessel, for in the rôle of merchant-man the Portchester Castle was steaming at a bare fifteen knots. Three miles away and broad on the starboard beam was the tramp, flying the red ensign. Already by means of the International Code she had "made her number". Her course was approximately parallel to that of the Portchester Castle, although her speed was less by a good five knots.

"Spot anything?" enquired Osborne of his chum, as Webb kept his binoculars focused at something almost midway and ahead of the two vessels.

"Yes," replied the Sub. "A periscope, or I'm a greenhorn. Here you are, Osborne, right in line with the foremast shrouds."

"By Jove, you're right!" assented the Lieutenant. "I can see it distinctly. Now who is she going for—the Two-Step or us?"

"The Two-Step, I fancy," replied Webb. "It looks to me as if the U-boat's periscope is trained in that direction."

Quickly the guns were manned. A warning signal, "'Ware submarine on your port bow", was sent to the tramp. The suppressed excitement grew as the Portchester Castle drew nearer to her as yet unsuspecting foe.

M'Bride was on the bridge at the time. Deliberately he delayed the order to open fire. The gun-layer could, he knew, easily knock away that pole-like object, but that was not enough. The U-boat, even when deprived of her "eyes", could dive and seek shelter until the danger had passed. Not until the submarine showed herself above the surface could a "knock-out" blow be delivered, unless the Portchester Castle could approach and ram her antagonist before the latter had time to submerge to a sufficient depth.

"Look!" exclaimed Osborne. "She's actually going to attempt to ram. Well, of all the cool cheek!"

The Lieutenant was correct in his assertion, for the plucky tramp, starboarding helm, was bearing down upon the vertical spar that denoted the presence of the otherwise hidden danger.

This manoeuvre interested Webb hardly at all. His attention was centred upon the periscope. For some time he had been keeping it under observation through his marine glasses. There was something fishy about it. He had seen partly 

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