Bowser's Sub

From the Super Mario Wiki

Bowser's Sub is a submarine featured in Super Mario 64 and its remake, Super Mario 64 DS. The submarine played a prominent role in the first mission of Dire, Dire Docks, entitled Board Bowser's Sub. Here, Mario had to climb atop the sub and reach the Power Star atop its bow. Though little is known about the sub, it can be assumed that Bowser's troops were in it. The sub disappeared after Mario defeated Bowser in the Bowser in the Fire Sea level. In Super Mario 64 DS, a Bill Blaster was added on the sub.