Confronting irregular challenges has been embedded in the United States Navy’s DNA since its earliest beginnings. While today’s Navy draws on a wider range of capabilities than ever before, addressing 21st Century security challenges demands a culture of continuous adaptation to ensure the Navy remains a relevant instrument of U.S. foreign policy and a key element within the broader U.S. strategic narrative that reassures friends and signals foes of America’s commitment to global stability. The Navy’s early history is replete with colorful examples of daring operations in response to irregular challenges. Lieutenant Stephen Decatur’s fearless mission to destroy the captured frigate PHILADELPHIA in Tripoli harbor in February 1804, and Lieutenant John McLaughlin’s use of his “Mosquito Fleet” to conduct joint counterinsurgency operations with Army units in the Everglades during the Second Seminole War in 1839 are but two vivid examples of Navy multipurpose forces confronting irregular challenges. Although Captain Alfred Thayer Mahan believed “…the Navy is best used to find and defeat an opponent’s fleet”, a review of U.S. naval history reveals a consistent theme of operations that did not engage an enemies fleet. Moreover, this historic trend continues to hold strong currency in today’s Navy missions, ranging from the Libyan intervention to providing humanitarian assistance to Japan and ballistic missile support to Europe. Today, three imperatives guide Navy efforts to confront irregular challenges: increasing understanding of this complex and dynamic security environment; improving the proficiency of Navy fleet forces to prevent and respond to irregular challenges; and enhancing the Navy’s interoperability with the Marine Corps, Coast Guard, Special Operations Forces, and other nation’s navies.