The "blimp" veered off once more, going back over her late course. As the "Grigsby" went about Darrin made out the tell-tale spread of oil on the waves.
"This is the real form of hunting," he exclaimed.
"Too bad, sir, that none of us thought of it before," remarked Ensign Andrews.
"We had to wait and learn," Dave explained. "That's the way that all progress in this war has been registered. We are fighting an ingenious enemy. Destroying the submarine mine-carriers, as we are doing today, won't end the planting of German mines. As soon as the enemy finds out how we are checkmating him he'll invent another scheme, which we'll have to discover before we can beat it."
Half an hour later the British aircraft located a third submarine.
"A big one, too," she signalled. "Following the same course."
"Mr. 'Blimp' might try a bomb himself," suggested Ensign Andrews. "I believe he carries a few."
"Not as powerful ones as we carry," Darrin answered. "Besides, he has to be at a greater altitude, when hunting submarines, than it's handy to drop a bomb from. There is too much margin of chance that the enemy craft will graze by when the bomb is dropped from the air. In our case, if we drop when directly over the Hun, there can hardly be a miss, and it's the dirigible's business to tell us when we are directly over the enemy."
In the meantime, on board the destroyer, all was made ready, and Dave followed the same tactics as before. This time, too, there was a normal explosion, though a solid hit was made and the submarine destroyed. Apart from the "blimp's" report there could be no doubt as to the destruction. The spread of oil on the surface of the sea told the story.
"If you and we hurry, we may bag another before dark," Dave sent by wireless, as the aircraft started back again.