On Okinawa, American forces reach Shuri, south of the former Japanese positions. Two battalions of US Marines reach the southeast edge of Naha.
The withdrawal of the 44th independent Mixed Brigade to the Kiyan line, 31 May 1945
On Okinawa, the US 6th Marine Division (part of US 3rd Amphibious Corps) encounters Japanese rearguards near Hill 46. Japanese forces pull out of Shuri.
The Shuri Line has fallen!
Final withdrawal of the 62d Division, 30 May thru 4 June 1945
Okinawa Campaign Background
American 10th Army intelligence did not realize this retreat was happening until 30 May and in addition, it did not know where the next line of defense would be. A program of interdictive artillery fire was started, but it did not reach as far south as the Kiyan line.
Heavy rains and mud plus, rear guard Japanese cave pill-boxes, made a rapid American pursuit impossible.
Between May 25th and June 4th 1945, the Japanese 32nd Army lost 20,000 of it’s 50,000 remaining troops retreating to the Kiyan Line.
This compares to the 7,000 the 32nd Army lost in it’s abortive May 4-5th 1945 offensive.
The loss in Japanese combat power was even worse than those raw numbers indicate. Only one in five of the combat troops present on 01 April were still able to fight. The loss of crew served infantry heavy weapons was worse. Only one-fifth of the original machine guns survived. Japanese hand grenades and mines were now almost exhausted.
Only one-tenth of the heavier weapons like 50mm mortars, 37mm and 47mm anti-tank guns, 70mm battalion level infantry support guns and 75mm field artillery survived.
The coming defense of the Kiyan line against American tanks would be compromised, between the shortage of mines and the lack of anti-tank guns. The approaches to and through the Kiyan line were good tank country, and despite killing close to 1/2 the American Sherman tanks in the invasion force, the starting force of Shermans was so large — the two Marine medium tank battalions (45 ea. M4 Sherman), four independent Army medium tank battalions (53 ea. M4 Sherman and 6 ea. M4 (105mm) assault guns) and one armored flame thrower medium tank battalion (54 ea. POA-CWS-H1 Flame thrower Shermans and 3 ea. M4 (105mm) assault guns) — that those left would be unstoppable.
The only bright spot was half of the IJA 5th Artillery Command’s large field guns were still intact, including sixteen 150-mm howitzers, because were kept in the rear with thus were relatively unscathed.
However, since this heavy artillery had only 1,000 rounds of ammunition per gun at the start of the campaign. Their remaining combat power was as limited as their ammunition.
According to Leavenworth Papers Number 18, Thomas M. Huber’s Japan’s Battle of Okinawa, April-June 1945
The Japanese withdrawal to fresh lines in the south succeeded in part because the Americans did not make an early concerted effort to break through the Shuri shell. On 26 May American aerial observers noted men, artillery, and armor moving south, but they also reported a large column moving north. This latter force was probably the IJA rear-area garrison units that were called up from the Chinen Peninsula to aid in the 25-26 May attacks on Yonabaru. Since the American analysts were not aware of an overall pattern of southerly movement, they concluded that the Japanese were using the bad weather to cover an overdue rotation of reserve and frontline troops.43
Visibility on 29 May was zero, and air observation was impossible. Nevertheless, by 30 May, because of vacated IJA positions found west of Shuri and other accumulating bits of evidence, U.S. Tenth Army intelligence finally reached a consensus that the Shuri lines were being abandoned. But the Americans did not know where the new lines were and assumed they were about two miles behind the old ones, just enough to straighten out the salients the Americans had built up on the east and west .44
American forces elbowed into Shuri on 31 May, completing the reduction of the formidable Shuri line. They realized by this time that they were dealing only with a rear guard. The American force prepared to pursue the Japanese southward on 1 June, but by this time, the 44th IMB, the last IJA unit in the vicinity, had already completed its withdrawal. Moreover, given the sheltered nature of the Japanese defenses, it was impossible for the Americans to move forward safely if even a few Japanese remained in the pillbox caves. Those last few had to be eliminated, and that inevitably took days. The problem remained even after the Shuri line fell, because the IJA 62d Division and the 24th Division’s rear guard both manned intermediate positions between Shuri and the Kiyan area. Even though the IJA screening forces were few, safe and rapid forward pursuit by the Americans was impossible. In the upshot, U.S. Tenth Army units were not aligned and ready to engage the new Kiyan lines until 6 June.45