A voyage in an undersea boat! What boy has not done so time and time again in his youthful dreams? The Submarine Boys did it in reality, diving into the dark depths of the sea, then, like Father Neputune, rising dripping from the deep to sunlight and safety. Yet it was not all easy sailing for the Submarine Boys, for these hardy young ''undersea pirates'' experienced a full measure of excitement and had their share of thrills, as all who sail under the surface of the seas are certain to do. The reader who voyages with him make look forward to an instructive as well as lively cruise.