is best speed. On deck he found Mackinder caught in a bight of
the hawser by which the other vessel had been towed. His leg was jammed
against the fairleader. Only one glance was required to show the boy that
serious injury had been done.

Without waiting for words, the lad stepped to the side of the fallen man.
Swinging his axe quickly, he struck at the taut bond of hemp. A shower of
sparks followed the ringing thud of the axe upon the steel deck.

Mackinder dropped back upon the deck, limp and helpless, as the singing
of the parted line told of his release.

With tender solicitude the boys mounted the ladder to assist their
injured friend to the room below. Scarcely had the boys gained the deck
when they were startled by a terrific explosion. As Ned afterward
declared, it seemed as if they had been caught in a volcano of water.

"What has happened?" queried Jack, releasing his hold upon Mackinder.

A flood of sea water descending upon the little deck prevented an answer
to his question. In a moment the lads were able to look about.

"Where's our 'U-13'?" asked Harry.

"Gone!" stated Ned, his voice trembling. "I'll bet that German torpedoed
it! I'm glad we are on this 'U-13'!"

Echoing this sentiment, the lads hastily proceeded to lower Mackinder
through the hatchway. This done, the injured man was deposited on a
couch, the hatch was closed, and Ned began first-aid ministrations.

"What course shall I hold?" asked Jimmie.

"Better head on a southwest course," stated Ned, briefly glancing up from
his work over Mackinder's leg.

"I can do that all right," responded Jimmie. "The gunboat and the
submarine can fight it out alone."

"We've got a clear field, Jimmie, so shove the little wagon along for all
she's worth," put in Jack.

Mackinder had been exercising wonderful command of himself, but in spite
of his best efforts a groan now and again escaped. The injured leg was
proving a painful matter.

"We'll do all we can for you, Mackinder," Ned offered, "but we need
better skill than is available here. Would it not be best to make at once
for some port where we can secure the services of a surgeon?"

Mackinder's only reply was a nod. His teeth were closed tightly to
suppress the cry of anguish from his hurt.

"Keep on the surface, boys," urged Ned as he went about making the man
comfortable with such simple means as were at hand. "I believe we are not
far from the coast."

Surrendering the wheel to Frank