Japanese land-mine technique has reached its highest point to date in the efforts of the enemy to lay mines on beaches as a defense against probable U.S. landing operations.

Recent island assaults in the Central Pacific have disclosed a trend toward antiboat and antivehicle beach-mining, a type of activity which may be encountered to an even greater extent in the future. Until now this defensive tactic has been met principally on comparatively small islands where suitable landing beaches have been limited, and where the Japanese have had ample time to construct strong defensive installations.

The mine most frequently encountered in beach areas has been the double-horn hemisphere mine. The detonators of this mine consist of two lead-alloy horns, each containing a vial of acid. When either horn is bent or crushed, the acid vial is broken. The acid then contacts battery plates and generates a current which detonates the mine.

This mine has been used by the Japanese in several ways. Usually the mines have been set so they would detonate when pressure was put upon trip wires connected to the detonating horns.

At Tarawa this mine was found emplaced in the shallow water off shore. They were set between posts and other antiboat obstacles, and trip wires were strung from the horns to the top of each adjoining obstacle.

During the landing on Tinian Island, hemisphere mines were found buried on the beach between the high and low water lines. In this position they were a hazard to boats beaching at high tide, and to personnel wading ashore from boats at low tide.

On other beaches many mines were found buried to horn depth in the sand and connected by trip wires strung between the horns of two or more mines. When wired in this manner, the weapons serve as antipersonnel as well as antivehicle mines.

Although these mines have been developed and used principally as an antiboat mine, it is not uncommon to find them emplaced several rows in depth on beaches and in the area just to the rear of the beach. When laid in this manner, they usually are set with a trip wire between mines, and constitute a hazard both to troops and to vehicles moving inland from the beaches.

To date the Japanese have tended to concentrate their efforts at mining to the beaches, and have neglected to use efficient inland minefields. This might be attributed to the characteristic Japanese defense doctrine which provides for the defeat of their enemies "at the water's edge," and does not envisage the possibility of an inland battle after a beachhead has been seized by the invading force.