What was the last amphibious operation of the Civil War?

The Capture of Fort Fisher was indeed the last major amphibious operation of the Civil War, taking place from December 1864 to January 1865. This operation was crucial because Fort Fisher was the primary Confederate fort protecting the port of Wilmington, North Carolina, which was a vital supply line for the Confederacy.

The successful amphibious assault by Union forces, combined with a sustained artillery bombardment, ultimately led to the capture of the fort. This not only effectively closed the port but also limited the Confederacy's ability to resupply its troops, contributing significantly to the Union's overall strategy to defeat the Confederacy.

The other options are significant events in the Civil War, but they do not fit the criteria of being amphibious operations. The Battle of Antietam and the Battle of Gettysburg were major land battles, while the Siege of Vicksburg, although it included some naval operations, primarily involved a prolonged land campaign rather than the joint land-sea assault that characterized amphibious operations.