Submarine warriors

the long version

"The fathers of twelve year-old Caroline Connery, Nick Wyatt, and their friends mysteriously disappear during a top-secret submarine mission. Not long after, Caroline receives a secret text message revealing the government's story that their fathers died in an accident was actually a cover-up. The two kids enlist the help of Caroline's grandfather--a retired Navy Admiral--and their friends to rescue all of the dads. A daring submarine theft results in the entire Pacific fleet chasing down the children with orders to sink them on sight. Upon finding their fathers, Caroline and Nick are confronted by an even greater terror when they come face to face with the Underworlders, a previously unknown species living beneath the ocean floor that are bent on the complete annihilation of mankind."--Page 4 of cover.