rt by the sound of
a cannon shot booming through the gathering darkness.

"What's that?" inquired Jack anxiously, jumping to his feet.

"I'll bet it's that bloomin' steamer we saw!" cried Jimmie. "That must be
another of those gun boats and they're chasing us!"

"I'll go up to the deck and see!" offered Ned.

"Be careful, don't let them get you!" warned Jack.

"I'll watch out for that," laughed Ned, mounting the iron ladder.

Directly the little group at the foot of the ladder were startled to hear
their companion's voice. A note of anxiety vibrated through his words.

"Boys," Ned cried, "there's a gunboat out there, and I think I see
another submarine. It looks to be like the 'U-13' for all the world. What
shall we do?"

"Here," urged Jimmie, "take the glasses and have a good look. If it is
that Dutchman, I'm for beating it out of here mighty quick!"

For a tense moment Ned gazed through the glasses at the strange vessels.
At length he lowered the binoculars and turned toward his companions.
With a shake of his head and a quick indrawing of breath, he said:

"It's the 'U-13' as sure as can be!"

"Let's go!" was Jimmie's only comment as he turned toward the switchboard
with outstretched hand.

"I'm with you!" declared Ned, quickly descending the ladder to join the
group. "Go ahead slow, though. Don't break the hawser, or we'd lose the
other vessel."

"Perhaps we would do better to abandon your vessel," Mackinder suggested
as he prepared to go on deck. "Let me have the glasses, if you please.
I'll look them over."

Jimmie paused, with his hand on the starting switch.

Suddenly all were startled by a cry from their host.

"Go ahead! go ahead!" he shouted down the hatchway. "That other fellow
has launched a torpedo at us!"

"Let go the line, then!" urged Ned. "We'll have to run for it! Full
speed, Jimmie!" he added.

Mackinder was casting off the hawser with rapid motions. Jimmie, in
response to Ned's command, threw the switch over. The "U-13" began to
gather headway.

All were startled to hear the report of a cannon shot. This was followed
almost instantly by a shriek from the man on deck.

"Mackinder's hit!" gasped Ned, turning a blanched face to his chums.
"What shall we do?"

As if in answer to his query, the voice of Mackinder reached the ears of
the lads.

"Bring an axe!" he shouted. "I'm fast in the bight!"

Wrenching an axe from its pocket on the bulkhead, Ned sprang up the
ladder at h