Super Mario Land did indeed have a level in which Mario piloted a submarine, as well as a later level in which Mario piloted a small plane. (Those levels offered an experience not unlike the Rush-Marine and Rush-Jet from later Megaman games.)
In general though, I found it to be a fairly underwhelming game that didn't measure up to the main Super Mario Bros series on the NES. (Although, in fairness: it was one of the very first GameBoy games, Nintendo actually created a new game with new enemies rather than attempting to port Super Mario Bros, it was indeed nice to play a Super Mario game on the portable GameBoy, and the aforementioned vehicle based levels were unique.)
The Super Mario Land series was much improved with its sequels though, which offered vastly improved graphics and game play, included better and more creative power-ups and enemies, and ditched the rather stock, one time alien overlord villain Tatanga for the far more amusing Mirror Universe / Earth-3 anti-Mario known as Wario!
