The narrative follows three adolescent members of a private submarine crew whose vessel is taken into naval service while they join a prize detail at Annapolis. Their adventures alternate between hands-on engineering work and sea cruises, exposing them to equipment failures, inventive rivals, waterfront scheming, and run-ins with military authorities. Episodes emphasize technical problem solving, loyalty among friends, and daring seamanship, culminating in inquiries and official judgments that test their competence and resolve as the young men help advance the practical use of submarine craft.