Jack hurried on deck.

In the distance the Ventura was plainly visible now.  Jack changed the course of the ship slightly, and after the vessel had gone half a mile he made out the form of a submarine lying close astern of the Ventura.

“By George!  They must see us,” he muttered.  “If the lookout on the U-Boat hasn’t espied us, surely some of the Germans on the deck of the Ventura must have done so.  Wonder why the submarine captain doesn’t sink the steamer and submerge.  Surely he is not going to risk an encounter with me.”

Nevertheless, it seemed that such must be the submarine commander’s intention, for the submarine showed no sign of submerging as the Essex bore down on her.

Through his binoculars Frank was now able to ascertain the fact that a struggle was in progress on the deck of the Ventura.  A dozen or more figures, closely interlocked, were scuffling to and fro across the bridge.  Frank gave an exclamation.

“I know what’s wrong,” he ejaculated.

“Well, what?” demanded Jack, turning to him.

“Why, the crew, or some of the crew, has jumped the commander of the submarine and his escort.  That’s why the officer left on the U-Boat doesn’t dare sink the vessel.  And the crew of the steamer is keeping the German and his friends so busy aboard that they haven’t had a chance to jump overboard.”

“By George!  I guess you’re right,” declared Jack.  “Now if they can hold them fifteen minutes longer we’ll get in the game ourselves.”

Again Jack altered the course of the Essex and approached the submarine at an angle from the Ventura.

“Forward turret guns there!” he roared.

It was the signal the men had been eagerly awaiting.  Quickly the signal “ready” was flashed in the forward turret.  The men were already at their posts.

“Range finders!” ordered Jack.

“Aye, aye, sir,” came the reply of the officer in charge of this work, and he calculated the range swiftly and passed the word to the captain of the gun crew in the forward turret.

“Fire!”

A heavy shell flew screaming across the water.

But the range had not been correct and the shell flew past the submarine.  Again the range was calculated, taking into consideration the first error.  Again the command to fire was given.

This time the range had been gauged perfectly and the shell must have gone home had it not been for one thing.

A moment before the command to fire was given, a torpedo was launched by the submarine.  Jack saw the torpedo come dashing through the water, and he was forced to order the helm over promptly to escape the deadly messenger.  This maneuver was made at the precise moment that the Essex fired for the second time, and consequently the shell again went wide.

Almost at the same instant Frank, who had kept his eyes glued to the deck of the Ventura where the struggle on the bridge had continued fiercely, uttered an exclamation of alarm.