Obstacles, Intelligence Bulletin, December 1942 (Lone Sentry)

1. INTRODUCTION

In addition to being well trained militarily, the Japanese are deceptive and cunning. They have used obstacles only on a limited scale thus far in this war because they have been mostly on the offensive in the land fighting. As they go more and more on the defensive in the coming months, the Japs are expected to use a wide variety of obstacles to block our advances. Our forces in the Solomon Islands, taking the offensive on a large scale, had to deal with numerous pit traps, most of which were mined and cleverly camouflaged.

Most of the information in this section, with the exception of that concerning road blocks, was taken from a captured Japanese manual on field fortifications. The manual does not go into elaborate details about obstacles, but all the pertinent data available is presented.

2. ROAD BLOCKS

In the Malaya and Burma campaigns, the Japanese frequently used road blocks to great advantage. Their success was largely due to these factors: the jungle or swampy nature of the terrain, the scarcity of roads, the necessity of the British using the few roads available because their forces were largely motorized, and the fact that the Japanese usually outnumbered their opponents.

The blocks, as a general rule, were hastily prepared and were not very strong. Most of them could be broken easily by a powerful frontal assault, led or supported by tanks. Breaking through one barricade, however, was usually not enough, because the Japanese used them in series--at Shwedaung, Burma, five barricades had to be broken on one road before the British could continue their march. The Japanese also made a practice of closing in on the roads behind the British, thus blocking them off from units farther back.

The siting of the Jap road blocks was invariably good. They were located at points where the road passed through dense jungle or other enclosed country, such as rice fields or swamps. The actual blocks or barricades were always concealed from frontal observation except at a very short distance. They were strongly covered by well-sited mortars, light machine guns, and antitank guns. These weapons were placed in defiles--behind ridges or in hastily constructed holes or trenches. The frontage held on each side of the road was comparatively short, partly owing to the nature of the country.

To destroy these road blocks and allow uninterrupted movement of vehicles, matériel, and personnel, the British in Burma found the following tactics to be the most feasible:

Because of the jungle nature of the area on both sides of the road, only strong frontal attacks on a comparatively narrow front should be attempted. The attack must be carefully prepared and supported by every ounce of firepower available. It should be supported by barrage fire from all available artillery and mortars. Some of these weapons should be available for searching fire against enemy mortars in case the latter are used. The infantry should attack in waves with strictly limited objectives, each wave halting on its objective and taking up an all-around defensive position to be held until the whole column has passed. If tanks are available, they should precede each successive leading wave of infantry at infantry pace. Each leading wave of infantry must, in its turn, employ shock tactics, combining grenades with the fire of submachine guns, machine carbines, and Bren guns, and with the use of bayonets. It is necessary to capture and hold both sides of the road throughout the area so that the enemy cannot return to his positions dominating the route. But because of the jungle terrain, it is not necessary to hold a wide area on both sides of the road--strips wide enough to keep the enemy from observing the road are sufficient.

3. ANTITANK

The Jap manual describes two types of tank traps, one a triangular trench and the other a round one. The round trap, designed to allow the entire tank to fall into it, requires more effort to construct than the triangular trench.

"Antitank obstacles are designed to lift up the front end of the tank and check its advance," the manual says. "Double-row obstacles may be constructed on gentle slopes, while single-row obstacles are sufficient on relatively steeper ground. Tank traps are more easily discovered on sloping ground if not camouflaged, and they are more easily destroyed when located."

4. ELECTRIC

Electric obstacles are used mainly to kill or wound personnel and horses, and to help slow or stop an enemy offensive.

The obstacles are constructed by technical troops. The wire usually is strung on dry, barkless poles, or on poles with all buried parts insulated with asphalt or coal tar. The wire is connected to a high-tension power source, which generates 1,000 to 2,000 volts (alternating current). Transmission wires are sometimes strung along the ground, or under the ground.

The obstacles are electrified when opposing forces launch surprise attacks. Ordinarily, the electricity is off when the opposition is reconnoitering. Occasionally, in order to deceive, the Japanese turn the current on during reconnaissances. In an actual attack following such practices, the Japs turn the current on in one sector and off in another.

In searching for electrical obstacles put up by the opposition, the Japs use a detector and make personal reconnaissances with as much secrecy as possible. According to their manual, they seek to determine the voltage used, the location of the electric source, and the nature of the obstacles.

The Japanese manual says the best way to destroy electrical obstacles is by the use of explosives, such as bangalore torpedoes. Other methods include cutting the wires and shooting them apart with tank fire. "All broken ends of the wire must be wound around posts or thrust into the ground so as to cut off the current," the manual states. "The demolition squads must be provided with rubber insulating gloves when carrying out demolitions. In addition, they must use nets, rubber boots, and other insulating devices in dealing with urgent demolitions."