Three-quarters of the earth is covered by the ocean; an actor capable of restricting access to the maritime domain is a threat to the prosperity of the entire international community. As the US is facing a rise in credible anti-access/area denial (A2/AD) threats, the United States Department of Defense started developing counter access denial strategies early in the twenty-first century. Access denial strategies are not a new defensive strategy; what makes access denial challenging on the modern battlefield is the dramatic improvement and proliferation of weapons capable of denying access to or freedom of action within an operational area. To develop an understanding of the current access denial threat, it is imperative to start by reviewing current US policy and strategy pertaining to access denial challenges, followed by a review of the counter-A2/AD strategies currently under development by the Department of Defense. Through a historical review of Japanese naval battles during the early twentieth-century, a framework to model possible future contests for control of the maritime domain is possible. The identification that control of the maritime domain is the prerequisite for assured access sets the condition for successful joint operations. To achieve assured access, a unified Department of Defense counter-A2/AD strategy must holistically balance the logistical requirements arising from the multitude of distributed operations, expand concepts that directly apply ground combat forces to the defeat of sea denial capabilities, and emphasize research and investment in rapidly produced low-cost technology that extends the range of counter-A2/AD capabilities.

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