The division remained on Hawaii for a number of months, during which time it was triangularized, with the 108th Infantry regiment being reassigned to the 40th Division. A division that has been triangularized has been given three infantry regiments instead of the four of a square division. This final reorganization dismantled the brigade structure and again dropped the division’s strength to 14,000 men. Following the reorganization, the 27th Division was shifted to Oahu, where it would relieve the 25th Infantry Division, which was slated to join the U.S forces fighting in Guadalcanal. For most of its time in Hawaii, the 27th was under the command of Brigadier General Ralph Pennel.
On November 20th 1942, the 27th Infantry Division embarked on its first combat assignment, the capture of the coral atoll of Makin. The 27th also had a new division commander, Major General Ralph Smith. Units from the 27th Division also occupied the Majuro atoll on February 1st 1944 and successfully assaulted Eniwetok Island on February 19th of the same year. In June 1944, the division landed on Saipan, where its regiments fought together for the first time as a full division. Following Saipan the division was rested and reinforced at Espirto Santo for seven months before any further operations. During this time the 27th received its final division commander, Major General George Griner Jr. On April 12th, 1945 the division landed on Okinawa, where it would remain until September when it was sent to Japan briefly for garrison duty. The division was mustered out in late December of the same year. Since its arrival in the Pacific, the 27th Infantry Division had suffered 1,512 killed in action, 4,980 wounded in action and 332 who later succumbed to their wounds.
General Smith had been removed from command following a dispute with the aggressive and eccentric Marine commander, General Holland "Howling Mad” Smith who had been in overall command of the Saipan invasion. Holland Smith claimed that Ralph Smith had disregarded orders and mishandled the 27th Division, prompting the relief order. Later court of inquiry showed that the charges were for the most part unsubstantiated and General Ralph Smith was quickly given a new command.
The 27th returned to the states for deactivation in December 1945, the longest serving National Guard unit.