[1] The listing's two contributing structures are two concrete bunkers built by the Japanese military early in 1944, in a small gully at a location where fresh water was present and where thick bamboo groves may have concealed the area from American military air reconnaissance and attack.

The position was attacked on August 11, 1944 by the 306th Regiment of the 77th Infantry Division of the U.S. Army.

"Throwing white phosphorus grenades and using pole charges and more than 400 blocks of TNT, they blew up the front of the caverns, closing them."

The bunkers were opened by American engineers three days later and 60 bodies were found, including that of General Obata.

[2] There are other abandoned concrete structures to hold water from Mataguac Spring, not far away, that were built by the U.S. Army Corps of Engineers, after World War II.