A carrier battle group (CVBG) consists of an aircraft carrier (designated CV) and its large number of escorts, together defining the group. The first naval task forces built around carriers appeared just prior to and during World War II. The Imperial Japanese Navy, IJN, was the first to assemble a large number of carriers into a single task force, known as Kido Butai. This task force was used with devastating effect since the Imperial Japanese Navy's Attack on Pearl Harbor.