Secret of the Sunken Sub (The Ladd Family Adventure Series #5)

Josh video tapes what he thinks is a diving whale off the Hawaiian island of Maui, but is actually the accidental sinking of a highly secret Soviet robot submarine. The Soviets are desperate to find the sub before the U.S. Navy does. Josh's confidence is betrayed by a new friend, causing the spies to do anything to make Josh reveal where he saw the sub sink.