The Union Navy is the term commonly used to describe the United States Navy and its acts during the American Civil War. Similarly to Union Army and just "Union", it referred to the union of the states in the United States Constitution.

It had two principal missions:

• Enforcing the Union blockade of Confederate seaports, interdicting Southern commerce.
• Capturing and protecting river systems, in conjunction with the Union Army.

Its most famous part of the war was undoubtedly the Battle of Hampton Roads, where the ironclad USS Monitor engaged the CSS Virginia.