They are pillboxes, a type of defensive fortification, built by the 48th Independent Mixed Brigade; 29th Division of the Imperial Japanese Army during 1941-1944, between Japan capturing Guam on December 8, 1941 from the United States and the U.S. recapturing Guam in 1944.

Its precise location is not disclosed by the National Register; it is listed as "Address Restricted".

It was built of steel-reinforced concrete including beach rubble, and, as of the NRHP listing date, was in "excellent" condition.

There are "impressions of tabi prints and a possible Japanese character" in the cement roof, which is about .25-metre (0.82 ft) thick.

These pillboxes were clearly designed to repel invaders coming from the sea.