In December 1941 Guam was defended by small U.S. Naval and Marine units as well as the Insular Force Guard.
Beginning on December 8, 1941, Japanese aircraft repeatedly attacked American defenses on Guam. On December 10, about 400 Japanese troops of the 5th Defense Force from Saipan landed on on the island. An additional 5500 men of the Japanese South Seas Detached Force made separate landings in the north, southwest and eastern shores of the island. Japanese troops quickly advanced and defeated vastly outnumbered defenders. After token post -invasion resistance, the U.S. Marines surrendered.
U.S. Marine losses were 5 killed and 13 wounded (including the prior Japanese air assault of the island, the Marines’ losses were 13 dead and 37 wounded). The U.S. Navy lost 8 killed, The Guam Insular Force Guards lost 4 killed and 22 wounded. One Japanese naval soldier was killed and 6 wounded.
About 274 officers and men of the US Navy , 153 officers and men of the US Marine Corps and 134 US civilians (nurses, priests, businessmen, etc.) were sent to Japan as prisoners of war.