But before another shell could be fired from the U boat, a column of foamy water shot up a couple of hundred feet into the air. For a brief instant the bow and stern of the submarine showed, tilted up at different angles to the surface of the water. Then, as the muffled roar of an explosion was borne to the ears of Blake and his companions, their antagonist simply vanished, leaving a maelstrom of boiling water to mark her tomb.
"Hurrah!" shouted Dick, the first of the delighted and astonished men to find his voice. "She's gone. Wonder what's happened?"
"One of her torpedoes gone off by accident, I expect," hazarded his chum. "It seemed like an internal explosion."
"At any rate, she's gone," observed Blake thankfully. "Now, lads, let's get on with the business, before there are a swarm of patrol boats on the scene. I shouldn't wonder if the noise of that explosion were heard fifty miles away."
Leaving Athol again on watch the others continued their interrupted labours; but before another ten minutes had elapsed came the watcher's doleful shout:—
"Another submarine!"
The new-comer had appeared upon the surface apparently without any preliminary investigation. At least Athol had not noticed the periscopes until the vessel rose at a distance of a cables length away.
She bore no number or distinguishing marks, but hardly was she awash when the conning-tower hatchway was opened, and a seaman dressed in a thick "fearnought" suit, appeared. Making his way aft he tugged at the halliards of a short flag-staff, and instantly a flag was "broken-out," fluttering proudly in the breeze.
It was the glorious White Ensign.
Others of the crew now appeared, as the submarine, forging gently ahead like an enormous porpoise, closed with the battleplane that she had so timely rescued. Then, slowing down, she came to a standstill ten yards to windward of the crippled aircraft.