Which function protects the ability to operate freely at sea?

The function that protects the ability to operate freely at sea is Sea Control. This concept encompasses maintaining maritime superiority to ensure freedom of movement and the ability to conduct operations without undue interference from adversaries. It involves the capability to deter or defeat hostile forces in a specific maritime area, allowing friendly forces to navigate and operate securely.

Sea Control is vital for enabling naval forces to execute various missions, including protecting trade routes, conducting amphibious operations, and supporting joint forces. By establishing and maintaining sea control, a nation can exert influence over maritime activities and safeguard its interests in international waters.

Other choices, while important in their own right, do not specifically address the primary objective of allowing unrestricted operations at sea. For instance, Humanitarian Assistance focuses more on providing aid and relief during crises, Deterrence relates to preventing adversary actions through the threat of retaliation, and Power Projection involves deploying military forces to influence events in another region, which doesn't directly pertain to maintaining freedom of operation in maritime environments.