This was the US geographical rather than operational codename for the long group of islands extending to the south-west from Kyushu in the Japanese home islands (1941/45).
Known to the Japanese as the Nansei Shoto (South-Western Islands), this islands group is a curving chain of widely spaced islands extending almost 650 miles (1045 km) to the south-west of Kyushu, the most southerly of the Japanese home islands into the East China Sea toward Formosa. The islands are part of Japan proper.
The Ryukyu Retto (Ryukyu islands group) comprises most of the islands of the Nansei Shoto, and the two names are often regarded as synonymous. The Ryukyu islands group comprises 161 islands, with a total land area of 1,792.33 sq miles (4642.1 km˛) in five major groups. From north-west to south-east, these five groups are the Osumi Gunto just off the southern end of Kyushu, the Tokara Gunto group of small islands, the Amami Gunto group of islands almost as large as Okinawa Gunto, the Okinawa Gunto separated from the next group by almost 190 miles (305 km), and the Sakishima Gunto large group comprising the Miyako Retto and Yaeyama Retto less than 100 miles (160 km) to the east of Formosa.
In addition to the Okinawa Gunto, whose main islands the US forces took in 'Iceberg' as their only target area in the Ryukyu islands group, the other larger islands of these groups were held by Japanese forces. In the Amami Gunto the 21st Independent Mixed Regiment defended Amami O Shima and Major General Toshisada Takada’s 64th Independent Mixed Brigade held Tokuno Shima. The Sakishima Gunto was defended by Lieutenant General Senichi Kushibuchi’s 28th Division and Major General Chuichiro Ando’s 60th Independent Mixed Brigade on Miyako Jima, Major General Tetsushiro Taga’s 59th Independent Mixed Brigade on Irabu Jima, and Major General Takeshi Miyazaki’s 45th Independent Mixed Brigade on Ishigaki Jima.