CONTENTS

[CHAPTER I. A MYSTERY]
[CHAPTER II. ON ACTIVE SERVICE AGAIN]
[CHAPTER III. A LESSON]
[CHAPTER IV. STRANGE WARFARE]
[CHAPTER V. THE END OF BLOSBERG]
[CHAPTER VI. WITH THE MOTORBOAT FLEET]
[CHAPTER VII. AN ENEMY]
[CHAPTER VIII. FRANK IN TROUBLE]
[CHAPTER IX. JACK TO THE RESCUE]
[CHAPTER X. LOST—THE STORM]
[CHAPTER XI. ON THE HUNT]
[CHAPTER XII. THE FIRST VICTIM]
[CHAPTER XIII. A DESPERATE VENTURE]
[CHAPTER XIV. WITH THE ENEMY]
[CHAPTER XV. PLOTTING]
[CHAPTER XVI. AN ENEMY SUNK]
[CHAPTER XVII. AN ARGUMENT SETTLED—TEMPORARILY]
[CHAPTER XVIII. MISTAKEN FOR AN ENEMY]
[CHAPTER XIX. THE TRAP IS SET]
[CHAPTER XX. THE TRAP IS SPRUNG]
[CHAPTER XXI. AT SEA AGAIN]
[CHAPTER XXII. TOWARD OSTEND AGAIN]
[CHAPTER XXIII. AN UNEXPECTED ENCOUNTER]
[CHAPTER XXIV. ANOTHER UNPLEASANT SURPRISE]
[CHAPTER XXV. DOOMED TO DIE]
[CHAPTER XXVI. MORE TROUBLE]
[CHAPTER XXVII. THE PIRATES REAPPEAR]
[CHAPTER XXVIII. THE BATTLE AND THE ATTACK ON THE U-6]
[CHAPTER XXIX. THE END OF A TRAITOR]

THE BOY ALLIES UNDER THE SEA.

CHAPTER I.

A MYSTERY.

"What I would like to know," said Frank Chadwick, "is just how long England intends to put up with the activities of the German submarines in the waters surrounding the British Isles."

"How long?" echoed Jack Templeton. "Surely you know that England is already conducting a vigorous campaign against them."