<p>Because I'm not sure how to paraphrase it well enough, here is a quote from the page on The Joker Wikia.
</p><p>" On one night, he and his men sneak down to the Gotham River and change the buoys, intending to trick a steamship into running aground like the famous battleship Missouri. The ploy works, and the ship becomes hopeless stuck in the muddy banks of the shallow river, allowing the Joker and his men to rob it of the diamond collection aboard."
</p><p>Here is the link to to the page.
http://joker.wikia.com/wiki/Batman_66
</p>