The Motor Boys Under The Sea is the 15th volume in the series. It was only a matter of time until the boys got a submarine, and that's what happened by the end of the book, even if they might have to return it. Sure, they could have bought one, but then what about the wreck of their dirigible/airplane, the Comet, over the ocean; an aggressive whale; a whacko German sub commander; a fight with a giant octopus on the bottom of the sea; and, the return of an incredibly-valuable family diamond necklace by Bob's uncle. Oh, and let's not forget Professor Snoggrass's search for a rare crab that almost ends up killing him and Jerry.
Clarence Young was a Stratemeyer Syndicate pen name. Howard Garis almost certainly wrote the series, although Stratemeyer usually provided his authors with an outline of the books. Garis and his wife, Lillian, wrote many children's books under their own name. They are best known for a series of books that featured the character of Uncle Wiggily Longears, an engaging elderly rabbit. Many of Garis' books were illustrated by Lansing Campbell. Garis and his wife, Lilian Garis, were possibly the most prolific children's authors of the early 20th century. Garis wrote many books for the Stratemeyers Syndicate as well, over a period of some 30 years.