The 1945 Invasion of Okinawa — the last major World War II engagement between the U.S. and Japan — was given what operational name by the U.S.?

The 1945 Invasion of Okinawa — the last major World War II engagement between the U.S. and Japan — was given what operational name by the U.S.?

Operation Flintlock
Operation Watchtower
Operation Iceberg
Operation Sandcrab
Operation Stalemate

The correct answer is Operation Iceberg