When U.S. Marines attacked Cape Torokina, on Bougainville Island, in November 1943, they found that the Japanese had prepared a system of defenses extremely well suited to the terrain (see figs. 9 and 10). Essentially, the defenses consisted of 25 bunkers disposed in depth and mutually supporting. Nine bunkers faced the west side of Cape Torokina and covered the west beach. Six bunkers faced and covered the east beach. Eight bunkers were situated from 50 to 100 yards behind the nine bunkers facing west, and covered them. Two additional bunkers covered the approaches to the rear of the inland bunkers and those on the east beach.

Figure 9. System of Japanese Bunker Defenses on Cape Torokina.

Each bunker was surrounded by a series of foxholes connected by deep, narrow trenches, which eventually led to the rear door of the bunker. The foxholes were intended to cover, not only the approaches to the particular bunker they surrounded, but also the approaches to neighboring bunkers. Machine guns within the bunkers were sited to fire diagonally along the beach or across the front of the probable avenues of approach; thus each bunker achieved cross fire with its neighboring bunkers, thereby attaining a "final protective line." A bunker usually contained two machine guns, with each gun laid on a fixed line. In no instance were two guns laid on the same line. The firing ports of the bunkers were very close to the ground.

The construction of the bunkers warrants a brief description. Each bunker was constructed of coconut and ironwood logs, from 18 to 24 inches in diameter, fastened together with a standard staple that the Japanese issue for this purpose. The log frame, about 14 feet square and having an interior height of 7 feet, then was covered with a dome of sand. The sand was piled so high that the roof was covered with 3 to 5 feet of sand at the eaves. The interiors of some of the bunkers were lined with sandbags to lessen the effect of explosives which might be fired or hurled into the bunkers.

Figure 10. Typical Japanese Bunker on Cape Torokina.

For camouflage, small palms and clumps of Bermuda grass were set into the sand covering the bunkers. The natural underbrush which covered Cape Torokina had been left standing. At first inspection, it seemed that the Japanese had made a serious mistake in not removing this underbrush, which presumably would restrict the defenders' fields of fire. However, as soon as one took up a position in a bunker or foxhole, it could be seen that the Japanese had cleverly prepared fields of fire by stripping the bushes of all branches and foliage up to 8 or 10 inches above the ground—a procedure they have followed in other areas, as well. As a result, the enemy was able to observe the feet of the attacking troops. Because the bushes had been left virtually intact, the supporting bunkers to the rear could not be seen at all from the beach; their presence was detected only when they fired on the attackers, who were in the act of breaking through the beach defense line and attempting to advance into the rear area.

The key to the Japanese defense of the west beach was an emplaced 75-mm regimental mountain gun, Model 41 (1908). Weighing 1,200 pounds, this gun measures 13½ feet over-all, and has a 50-inch barrel. The gun has an effective range of 2,100 yards, but its traverse is limited to 6 degrees. This weapon was sited within 5 yards of the high-tide mark for anti-boat defense, and its emplacement was well protected by two nearby bunkers and the usual system of foxholes and connecting trenches. Two hundred rounds of high-explosive shells had been stacked inside the gun emplacement, ready for firing. During the U.S. landing, this gun fired approximately 50 rounds, but, because of its limited traverse and the poor gunnery of its crew, its performance obviously was not as effective as the Japanese must have intended when formulating their defense plan.

The defense force assigned to Cape Torokina consisted of a reinforced infantry company. Its total strength, on the day the U.S. Marines landed, was 270 men.

The following small arms were used in the defense: the 6.5-mm rifle (1905); the 8-mm pistol; the 6.5-mm light machine gun (1922); the 6.5-mm light machine gun, Type 96 (1936); the 7.7-mm heavy machine gun (1932); the heavy grenade discharger, Model 89 (1929), firing the high-explosive shell, Model 89; and, finally, the fragmentation hand grenade, Model 91 (1931).