The last Marine Division ever to be activated, the 6th was formed on 7 September 1944 on Guadalcanal from the “First Provisional Marine Brigade,” which was manned by troops from the 4th and 22nd Marine Regiments. To their number would be added two more Marine Regiments, the 15th and the 29th, and for the next six month these regiments and their supporting units trained for what would be their only campaign action during the war: the invasion of Okinawa.
For the Japanese, the battle to defend Okinawa amounted to nothing less than a last stand: the island represented the last stepping the U.S. needed to base its operations leading up to an invasion of the Japanese mainland. As part of the III Amphibious Corps, the 6th Marine Division landed at Hagushi Bay with an initial objective of seizing Yontan Airfield, which it achieved in very short order; within two weeks, the Marines had advanced nearly 60 miles from their landing area and had cleared the northern half of the island.
But Army forces in the south were having difficulty making headway against the Japanese defenders, due in no small part to the tactical advantages the terrain offered for defensive warfare. In the end, the Marines were left with almost no other option than to conduct a brutal and bloody head-on offensive, with the 6th assigned to capture three hills called the Sugar Loaf Hill Complex that anchored the Japanese Shuri defensive line. After a week of fighing, Sugar Loaf was taken, but the cost had been high: in a single day (May 16), the Division suffered over 500 casualties and over 2600 killed or wounded during the action to expel the defenders.
Following the end of fighting on Okinawa, the Division was sent to Guam to begin preparations for an invasion of Japan that thankfully never took place. When it was inactivated on 1 April 1946, it became the only USMC Division that did not set foot in the United States during its existence.