The "U" boat was evidently standing by to cover the flight of the Zeppelin should any cruiser stand in pursuit, for the airship was flying comparatively low, instead of the usual altitude of ten thousand feet, when annihilated by the "Anzac's" fire. Having witnessed the destruction of the Zepp., the "U" boat had approached the monitor with the intention of avenging the loss of the air-raider. She had no idea that the "Anzac" was aground, for by this time she was almost waterborne and lay on practically an even keel; while, since the whole of the sandbank was submerged, there was no indication of shallow water.
Nevertheless it seemed as if the monitor would fall an easy prey to the German torpedo, for there was not a single gun that could be brought to bear in the direction of the submarine.
Tressidar was not kept long in suspense. The feather-like wake of the approaching weapon was clearly visible as the torpedo made unerringly towards the immovable target.
"Stand clear there, aft!" shouted the sub.
Those of the crew who had been watching the approach of the submerged weapon promptly scurried across the deck so as to be as far from the point of impact as possible. Of serious damage to the monitor there was little fear, owing to the complex nature of her bulging sides. The loss of twenty feet of side plating would matter but little, since the buoyancy of the monitor would not be appreciably altered.
But the expected explosion did not occur. Set to run at a depth of twelve feet, the torpedo struck the sandy bottom at a distance of between eighty and a hundred yards short of the target.
For another twenty yards it ploughed through the sand, until its delicate rudders were damaged by tearing through the comparatively hard substance. Then with an erraticity that torpedoes have been known to display, the weapon made a sharp curve, and rising to the surface continued its undecided way like a hydroplane, its course being marked by a line of spray in its wake.
Again the monitor's crew cheered—this time ironically. The shoal that had proved a stumbling-block was now guarding the stranded craft in no uncertain manner.
After a lapse of a quarter of an hour the submarine cautiously poked her periscopes above the surface, although quite half a mile from the spot where she had previously dived. Once more she fired a torpedo, with almost the same result, for instead of turning on impact with the shoal, the weapon struck nose first into the sand and remained there.
The commander of the "U" boat was evidently puzzled. He could not understand why the two torpedoes should have missed the mark; he was also at a loss to account for the fact that the British vessel had not attempted to open fire.