Naval Governor of Guam George McMillin surrendered to the Japanese forces around 7:00 a.m. on December 10, 1941, ceding control of the island.

Specifically, Commander Hayashi Horace, who was one of the military leaders during the Japanese invasion in December, made Agana's former governor's palace the headquarters for the kenpeitai.

The task was at first thought to be a swift and easy one, as the population of Guam was small; however, these Japanization efforts later faced difficulty, supposedly due to the Americanization of the Chamorros during the prior 40 years under US control.

With an American invasion threatening, the Japanese Army returned to Guam, bringing with it a new, stricter form of government, the kaikontai.

[1] Social activities were terminated, schools were closed, and Chamorro men, women, and children over the age of 12 were forced to work long hours in the fields, repair or build airstrips and defense installations, and dig hundreds of Japanese cave shelters, many of which are within the boundaries of War in the Pacific National Historical Park on Guam.

Without warning, 10,000–15,000 Chamorros of all ages were forced to march, with only the belongings they could carry to camps in Guam's central and southern jungles.

Despite hardships, however, incarceration proved to be a blessing in disguise for those who survived the camps, as had they not been moved, many Chamorros would have been killed by the American bombs and Japanese crossfire.

Obata withdrew his troops from the south of Guam, planning to make a stand in the mountainous central part of the island.

But with resupply and reinforcement impossible because of American control of the sea and air around Guam, he could hope to do no more than delay the inevitable defeat for a few days.

Rain and thick jungle made conditions difficult for the Americans, but after an engagement at Mount Barrigada from 2 to 4 August, the Japanese line collapsed and the rest of the battle was a pursuit to the north.

The results of the Japanese military occupation led to strong anti-Japanese views from the Chamorros that continued until late 1960s.

Since June 2006, the US Congress, the House Judiciary Committee, and the Department of Justice have worked together to approve a bill for Chamorro war reparations.