submersible

"During World War II, submarines played a crucial role in naval battles. "

"communication of a secret"

"The exploration of new hiking trails is a favorite family activity. "

"The aquifer's underwater supply of fresh water is crucial for the town's water system. "

"My brother is primarily a student; he spends most of his time studying. "

"The library books are classified by subject, so finding a book on history is easy. "

"Scientists use submersibles to study deep-sea creatures. "

"The new law is retroactive to January 1st, meaning it applies to actions taken since that date. "

"The submarine traveled deep beneath the waves. "

"Biologists study living things, from tiny bacteria to giant whales. "

"The new legislature passed a resolution retroactively legalizing the actions of the revolutionaries that brought them to power."

"The organization provides nonmilitary aid, such as food and medicine, to the refugees. "