S.D.M.G.

The S.D.M.G is a straight upgrade to the Megashark, with the same fire rate and ammo usage bonus, except with a noticeably higher damage output.

Possibly not obtainable yet. (See: http://www.terrariaonline.com/threads/about-reds-vanity-set-and-s-d-m-g.108174/#post-2296339)

Trivia

 * This item's description may be a reference to the indie title Edge of Space, in which rocket propelled sharks appear as an enemy.
 * This item could also be a reference to the book "The Hitchhiker's Guide to the Galaxy" in which all of the planet's dolphins flew off into space to avoid the iminent destruction of Earth.