Exercise Mainbrace was the first large-scale naval exercise undertaken by the newly established Allied Command Atlantic (ACLANT), one of the two principal military commands of the North Atlantic Treaty Organization (NATO). It was part of a series of NATO exercises jointly commanded by Supreme Allied Commander Atlantic Admiral Lynde D. McCormick, USN, and Supreme Allied Commander Europe General Matthew B. Ridgeway, U.S. Army, during the Fall of 1952.