At a sign from Denbigh the flight-sub trimmed the elevating planes. Up climbed the machine till at an altitude of six thousand feet she was visible from the distant monitors. Then she commenced to cut figures of eight, while Denbigh began to call up the _Paradox_ by wireless. Having made certain that the monitor had gauged the required distance the sea-plane volplaned to within a thousand feet of the ground. The receiving telephones fixed to Denbigh's ears began to emit faint sounds that in Morse spelt out the words, "Stand by to register". Twenty seconds later a lurid flash, followed by a terrific cloud of yellow and black smoke, leapt skywards from a spot in the mangroves. In spite of her altitude the sea-plane rocked violently in the torn air. For a moment Denbigh thought that the machine was plunging helplessly to earth. The gentle tapping of the wireless receiver recalled him to a sense of duty. "How's that?" spelt the dot-and-dash message. Where the shell had burst a dozen or more trees had been literally pulverized. Others, their trunks lacerated by the explosion, had toppled at various angles against those that had withstood the shock. The "hit" was roughly two hundred yards beyond the screened battery. From beneath the foliage covering the emplacements men peeped timorously. A dull-grey figure, bent almost double, was running for shelter. It was one of the German sentries. "Right direction; two hundred yards over," wirelessed Denbigh. Another heavy projectile screamed on its way, passing some hundreds of feet beneath the seaplane. It burst; but the sound like that of its predecessor was inaudible to the pilot and observer. The action of the detonating shells reminded Denbigh of an animated photograph, so effectually and silently did the work of destruction appear. "A hundred yards short," registered the sub. "Then how's this?" was the rejoinder. Fairly in the centre of an emplacement fell the twelve-hundred-pound shell. High above the mushroom cloud of smoke flew fragments of wood and metal. When the dense vapour had drifted away in the sultry air it was seen that the work of that gigantic missile was accomplished. A gaping hole fifty feet in diameter marked the place where the carefully-screened quick-firers had been. Round the edge of the crater were smouldering sand-bags hurled in all directions like small pebbles. The two guns, dismounted, were sticking up at acute angles in the debris, their mountings shattered into fragments of scrap-iron metal. There was no sign of life in the crater, nor in the partly uncovered dug-outs in its vicinity, but from a neighbouring position poured swarms of Germans, half-dazed and terrified by the explosion that had shaken their subterranean retreat like a severe earthquake shock. The _Paradox_ had completed her particular job.