The development of the U.S. Navy carrier battle group can be traced to the 1920s and was initially based on previous experience grouping battleships and other major surface combatants. In World War II, administratively, aircraft carriers were assigned to carrier divisions (CARDIVs). Operationally they were assigned to Task Forces, of which Task Force 11, Task Force 16 and Task Force 17 perhaps gained the most fame for their roles in the Battle of the Coral Sea and the Battle of Midway. The single-carrier battle group was born with the military draw down that followed World War II. Carrier Division 1 was redesignated Carrier Group 1 on 30 June 1973, and seemingly all Carrier Divisions were redesignated Carrier Groups on that date. Throughout the 1990s, the U.S. Navy's aircraft carrier groups were officially referred to as Carrier Battle Groups (CVBGs), and were commanded by either flag officers called Cruiser-Destroyer Group (CRUDESGRU) or Carrier Group (CARGRU) commanders. In the summer of 1992, the U.S. Navy instituted a concept that mandated greater task group integration of naval air and surface warfare assets into a more permanent carrier battle group structure. Each of the Navy's 12 existing carrier battle groups consisted of an aircraft carrier; an embarked carrier air wing; cruisers, destroyer, and frigate units; and two nuclear-powered attack submarines. On 1 October 2004, carrier groups and cruiser-destroyer groups were redesignated carrier strike groups. The change in nomenclature from 'Battle' to 'Strike' appears to have been connected with an increasing emphasis on projecting air power ashore; the change acknowledged that battles at sea on the Battle of Midway model were becoming more unlikely. Carrier strike groups are tasked to accomplish a variety of wartime missions, as well as a wide variety of functions in situations short of war. The peacetime mission is to conduct forward presence operations, to help shape the strategic environment, deter conflict, build interoperability with allies, and respond to crises when necessary. The U.S. Navy provides a regular rotation of strike groups overseas, typically for six-eight months, based on the needs of Unified Combatant Commands that request strike group capabilities in their respective area of responsibility (AOR). The ships in the group often "disaggregate" from the carrier, performing missions hundreds or even thousands of miles away. The missions of the carrier strike groups include:  CSGs are not restricted to a specific composition and can be modified depending on expected threats, roles, or missions expected during a deployment, and one may be different from another.