Monitor vs. Virginia — World's First Ironclad Battle
The Union's newly arrived USS Monitor battled the CSS Virginia (Merrimack) in history's first fight between armored warships. Neither vessel could penetrate the other's armor, and after four hours both withdrew. It was a tactical draw but a strategic Union victory.
The battle made every wooden warship obsolete and launched a global arms race in ironclad construction that transformed naval warfare permanently.
Outcome
Draw — neither ship sunk; Virginia never threatens Union fleet again