Danny Dunn on the Ocean Floor

Danny Dunn accidentally helps the professor develop a new super-strong plastic, and he and his friends get to go along on a trip to Mexico to try out a bathyscaphe made with the material. I'm a bit uncomfortable with one interaction with a kid from Mexico whose uncle is known as El Bagre and Danny assumes "Bagre" is their last name. The science isn't too terrible but of course dated, and there's a side plot about the languages of fish.