Final answer:
The Union's goal in capturing Port Royal near Hilton Head was to launch a blockade of the important harbor at Charleston to cut off Confederate supplies and make it a base for future military operations.
Step-by-step explanation:
The Union captured Port Royal near Hilton Head to establish a blockading presence to control Charleston, an important harbor during the time of the American Civil War. This strategic win allowed the Union to launch a blockade of Charleston, which aimed to squeeze the lifeblood out of the Confederate supply lines, as well as to prepare for further military campaigns in the South. Learning from history, General Clinton during the Revolutionary War opted for an overland assault on Charleston rather than face its formidable coastal defenses directly. The siege and capitulation of Charleston in 1780 under British forces led by Clinton was a significant blow to the American revolutionaries.