Nevertheless he was wary. With the idea of drawing the monitor's fire, he released one of the communication buoys, towing it a hundred yards astern of the submerged craft. The resistance of the buoy caused a decided feather of foam that could not escape the eyes of the crew of the monitor. At the end of five minutes the buoy was drawn under the surface and taken on board the "U" boat again, by means of an automatic winding machine and a system of "air lock" doors. Examination showed that the relatively easy target was untouched.
Hence the commander of the German submarine came to the correct conclusion that the monitor was not capable of defence. Again the periscopes appeared above the surface and a prolonged examination of the British vessel was made. The German officers soon came to the decision that it was safe to rise and attack the monitor by shell fire, provided the "U" boat kept on the starboard quarter of her enemy.
"There she is, sir!" reported a petty officer to Tressidar, as the "U" boat rose to the surface at a distance of nearly two miles off.
Glasses were brought to bear upon the submarine, and it was then seen that the Germans were preparing to use their two "disappearing" guns. To reply was impracticable, for the submarine was well beyond effective rifle-range, and the sole serviceable turret gun could not be trained sufficiently abaft the beam to bear upon the enemy.
"Action stations!" was the order. Since the crew were without present means of offence or defence, all they could do was to take cover behind the armoured parts of the ship and "take their gruelling "; but every moment the tide was rising, and before long it would be possible to back off the shoal, turn and bring the gun to bear upon the Hun.
With little delay the "U" boat opened fire. The first half-dozen shells flew either above or wide of the monitor, but presently the small but relatively powerful missiles began to find a mark.
From his post in the conning-tower, which, in spite of the fractured dome, was proof against the small-calibre shells, Tressidar watched his opportunity. He made no effort to get the "Anzac" off the shoal until he felt certain that she would glide off without difficulty. Then, he hoped, there would be time to train the 14-inch gun on the submarine before she had a chance to trim for diving—and only two rounds for that particular weapon remained.
The gun, already loaded, was trained as far aft as possible, so that the moment the monitor swung round it could be brought to bear.
A leadsman, risking the flying fragments of shell, ran forward and, throwing himself at full length upon the low fo'c'sle, took soundings.
"By the mark two less a quarter," he announced.