Keen eyes swept the shining uneasy plain.

[Sidenote:  How a submarine crew takes orders.]

Meanwhile, some seventy feet below, the Z-3 manoeuvred, killing time.  The phonograph had been hushed, and every man was ready at his post.  The prospect of a go with the enemy had brought with it a keen thrill of anticipation.  Now, a submarine crew is a well-trained machine.  There are no shouted orders.  If a submarine captain wants to send his boat under quickly, he simply touches the button of a Klaxon; the horn gives a demoniac yell throughout the ship, and each man does what he ought to do at once.  Such a performance is called a “crash dive.”

“I’d like to see him come up so near that we could ram him,” said the captain, gazing almost directly into the sun.  “Find out what she’s making.”

[Sidenote:  Getting up speed.]

The engineer lieutenant stooped to a voice-tube that almost swallowed up his face, and yelled a question to the engine-room.  An answer came, quite unheard by the others.

“Twenty-four, sir,” said the engineer lieutenant.

“Get her up to twenty-six.”

The engineer cried again through the voice-tube.  The wake of the vessel roared like a mill-race, the white foam tumbling rosily in the setting sun.

[Sidenote:  Seventy feet below the surface.]

Seventy feet below, Captain Bill was arranging the last little details with the second in command.

[Sidenote:  The plan of attack.]

“In about five minutes we’ll come up and take a look-see [stick up the periscope], and if we see the bird, and we’re in a good position to send him a fish [torpedo], we’ll let him have one.  If there is something there, and we’re not in a good position, we’ll manoeuvre till we get into one, and then let him have it.  If there isn’t anything to be seen, we’ll go under again and take another look-see in half an hour.  Reilly has his instructions.” (Reilly was chief of the torpedo-room.)

[Sidenote:  Wreckage all about.]

“Something round here must have got it in the neck recently,” said the destroyer captain, breaking a silence which had hung over the bridge.  “Didn’t you think that wreckage a couple of miles back looked pretty fresh?  Wonder if the boy we’re after had anything to do with it.  Keep an eye on that sun-streak.”

[Sidenote:  A crash dive to avoid a destroyer.]

An order was given in the Z-3.  It was followed instantly by a kind of commotion—­sailors opened valves, compressed air ran down pipes, the ratchets of the wheel clattered noisily.  On the moon-faced depth-gauge, with its shining brazen rim, the recording arrow fled swiftly, counter clockwise, from seventy to twenty, to fifteen feet.  Captain Bill stood crouching at the periscope, and when it broke the surface, a greenish light poured down it and focused in his eyes.  He gazed keenly for a few seconds, and then reached for the horizontal wheel which turns the periscope round the horizon.  He turned—­gazed, jumped back, and pushed the button for a crash dive.