Captain Jack's greatest dangers came through the wiles of charming
women spies, especially one beautiful young Russian woman, Mlle. Sara
Nadiboff, easily the most clever of all international spies. Yet the
cleverness of the submarine boys carried them successfully, and with
highest honor, through the gravest situations in their eventful, young
careers.

Just at this particular time the young men had been going through dull
days. Beyond the fact of the mere presence of the heavily charged
torpedoes at the shipyard there had been nothing like excitement, for
some time. This dullness, however, was destined to turn, suddenly,
into the most intense and exciting activity.

As Jack pushed open the outer door of the office building of the
shipyard, Jacob Farnum, the owner, happened to be bustling through the
corridor.

"Hallo, boys!" came his quick, cheery greeting. "I was just about to
send for you."

"Any word," queried Jack, good-humoredly, "as to when that cold-molasses
naval officer is going to be here!"

From within the office sounded a light laugh.

"You'll see him shortly," grinned Mr. Farnum. "But come in, boys."

As the three submarine boys entered the office, in a group, their
glances fell upon two men, in the uniform of United States sailors,
standing at ease near the door. In a chair near Mr. Farnum's desk sat