Pacing alertly up and down the bridge, Peter was approached by a yeoman of signals. "Message from Flag, sir," he reported. The lieutenant took the signal pad into the chartroom. Then he gave a low whistle. The sensitive microphones on board the _Royal Oak_ had detected the approach of a large number of aircraft, bearing north-west by north. That meant that, assuming the aircraft were the Rioguayan flying-boats, the hostile forces had made a wide detour and were approaching over San Valodarian territory. "Now we're going to see something," commented Peter, as he passed the message to a side-boy to convey it to the Skipper. The rest of the fleet had been simultaneously warned by General Signal. Every searchlight was "running", although carefully screened; and in conjunction with each searchlight was a "Strong" anti-aircraft projector. As a precautionary measure, the crews of the quick-firers were called to action stations, but already there was sufficient confidence in the rays to warrant the assumption that the forthcoming task would not require the aid of gunnery. Throughout the darkened fleet an uncanny silence prevailed. The night was starless. There was a flat calm. The conditions for microphone detector work were excellent. Nearer and nearer came the hostile flying-boats, their direction and distance being so accurately recorded that they derived no advantage by delivering a night attack. At length the dull rumble of their propellers became faintly audible. In spite of devices calculated to muffle the noise, it was impossible to smother the beats of fifty or sixty aerial propellers working in unison. "Bearing 55 degrees; elevation 22 degrees," announced the range-finding, officer at the searchlight director station. Then, fifteen seconds later: "bearing 60 degrees; elevation 25 degrees." [Illustration: A BLAZE OF DAZZLING BEAMS _Page_ 297] Not until the elevation increased to 30 degrees were the searchlights to unmask. The period of suspense seemed interminable, although the flying-boats were known to be approaching at well over a hundred miles an hour. "Bearing 90 degrees," came the level, even tones of the range-finding officer; then in a louder voice that seemed to indicate that a slow job had at last been completed: "Elevation 30 degrees." Within the space of five seconds, every searchlight of the fleet was flashed obliquely into the darkness. The air was one blaze of dazzling beams, spread fanwise lest any daring and cunning airman should attempt to approach from an independent direction. Eight miles off could be discerned the almost mathematical formation of the hostile air squadrons. They wavered when the beams fell athwart their path, which was probably owing to the pilots being temporarily blinded by the sudden glare. Then they recovered formation and came on. A red rocket soared skywards from the flagship. It was the signal to let loose the rays.