The Battle of Biak Island came about after a succession of Japanese defeats in 1943 and 1944 along the northern coast of New Guinea. Biak became a Japanese stronghold, which they were determined to hold to the last man. Unknown to the advancing Allies, the Japanese began fortifying the island and when the Allies invaded on 27 May 1944, the Japanese put up a fierce defense. The only tank vs. tank battle in New Guinea occurred on Biak, where Japanese Ha-Go light tanks were knocked out by American Sherman tanks. Japanese soldiers were well entrenched in the interior of the island in limestone caves and fortifications, a trend that would be seen again in islands like Palau. These entrenched troops fought an excellent defense and the casualties at Biak were high - for the American Army, 435 KIA and 2,360 WIA. The Japanese lost an estimated 6,125 KIA, with 460 POWs, and 360 Formosan POWs.