On December 10, 1941, the 400—man garrison on Guam was overwhelmed by 5,000 Naval Marines of the Imperial Japanese Navy in a few hours of fighting. Guam would not be the scene of fighting again until 1944.
By that time, the United States Pacific Fleet had made good their losses at Pearl Harbor and even their losses in the Solomons. It is testimony to American industry that while landings were made in Normandy, another fleet was anchored off Guam in the Marianas.
The landings began on July 21, 1944. The Americans, again using a combined Army and Marine force, ran into heavy fire on the beach. The fighting was savage, with the next two days seeing a slow march inland by the invading Americans.
On the night of July 25—26, 5,000 Japanese charged the American lines, which resulted in the death of over 2,500 Japanese. The Americans both dreaded and welcomed expected Banzai charges, which often speeded up the occupation as they killed most defenders in open ground instead of prepared defensive positions. Assaulting concrete bunkers always meant more casualties.
Seabees, construction battalions that could fight with the landing force, began constructing the airfields that the B—29s would use to burn Japan’s cities. Eventually thousands of aircraft of all types would be based in the Marianas.
Japanese survivors that escaped into the jungle continued to harass the Americans. The last Japanese soldier on Guam did not surrender until the 1970s.