Operation Stimulate

'Stimulate' was the US geographical rather than operational codename for Rota island in the Mariana islands group of the central Pacific (1941/45).

Rota lies 47 miles (75.5 km) to the north-east of Guam and 69 miles (111 km) to the south-west of Saipan, and was the southernmost and nearest of the Japanese-mandated islands to Guam, a US possession currently under Japanese occupation. Rota is 11.8 miles (19 km) long on its north-east/south-west axis and 3 miles (4.8 km) wide, and possesses an area of 33 sq miles (85.5 km˛). The island is steeply mountainous, and its highest elevation is 1,624 ft (495 m) at Mt Manira on its south-western end. Rota has a rugged coast faced with cliffs and lacks a harbour, but the open Sosanyaya Bay indents the island’s south-western end. The island’s population in 1944 was small, the largest village being Songsong on the south coast with fishing and sugar cane cultivation as its primary occupations.

It was at Rota that the Japanese forces for the invasion and seizure of Guam made their rendezvous after departing Haha Jima and Saipan on 9 December 1941.

By the time of the US 'Forager' assault on the Mariana islands group, the Japanese built an airfield near the north-east end of Rota, and had scheduled their 50th Regiment to move to Rota on 15 June 1944 as the island’s garrison, but the appearance of the US invasion force off Saipan led to its retention on Tinian. However, Major Shigeo Imagawa’s 1/10th Independent Mixed Regiment was despatched from Tinian on 23 June to garrison Rota, and was soon followed by the 3/18th Regiment as a counter-landing force for Saipan or Guam, but the latter was soon returned to Guam as the combination of sea conditions and US had rendered the plan impractical.

Rota was subordinated to the Southern Marianas Army Group, otherwise known as Lieutenant General Takahina Takeshi’s 29th Division on Guam until the latter fell on 10 August 1944. It then came under the control of the Japanese command on Pagan island. The Japanese garrison of 1,000 soldiers, 500 naval air service personnel, and 500 labourers then faced the prospect of sitting out the rest of the war.

During the war’s final stages, Rota was occasionally bombed by aircraft of the US Navy in an attempt to silence its radio transmitter, which was providing warning to the Japanese home islands when Boeing B-29 Superfortress heavy bombers took off from Tinian, Saipan and Guam, but US troops attempted no landing. On 2 September 1945, one hour after the surrender of Japan, a detachment of the US Marine Corps under Colonel Howard N. Stent arrived on Rota to accept the surrender of the Japanese garrison, which by that time totalled 947 army and 1,853 navy personnel.