If we’re ever going to explore the only celestial body in our solar system with surface bodies of liquid, we’re going to need a sea-worthy vehicle. Luckily, NASA is all over the niche space submarine market.
Titan, a moon on Saturn, has lakes and seas of liquid methane, which NASA is thinking of exploring by 2040. So, instead of rover like the Mars missions use, they will need a submarine. NASA explains the reason for the mission this way: