Secret Mission: How the Germans Brought Hollow-Charge Technology to Japan

Secret Mission: How the Germans Brought Hollow-Charge Technology to Japan


ABOVE: The seaman’s book of Colonel Niemöller. He travelled to Yokohama aboard the blockade runner “Tannenfels” and covered as a paymaster.

In the course of World War II the German Reich supported its allies with weapons, ammunition and equipment of various types. Most of these weapons were put into service unchanged or with only slight modifications. Among these, there were also a total of 70,879 complete sets of Gewehrgranatgeräte (rifle grenade launchers). It cannot be established exactly to which countries these launchers had been delivered, but three allies–Finland, Italy and Japan– not only issued them to their troops, they even copied them.

At the time of Japan’s attack on the U.S. naval base at Pearl Harbor on 7 December 1941, the bolt-action rifle Arisaka Meiji 38 in caliber 6.5mm (introduced in 1905) was the standard weapon of the Japanese infantrymen. But it was already hopelessly out of date, and the ammunition no longer met the requirements. A lot of experimental work was done with various calibers and types of ammunition, and the result of this research, the bolt-action rifle M.99 in caliber 7.7mm, was officially introduced in 1939.

The cluster bomb, developed on the basis of the hollow-charge anti-tank rifle grenade, was dropped from containers with a capacity of 30 respectively 72 bombs.

In the same year a rifle grenade cup launcher called “Type 100” was adopted by the Army. Depending on the weapon, high-explosive grenades could be fired at distances between 75m and 100m. To avoid the introduction of a special propelling cartridge, the Japanese were looking for a way to launch grenades by use of standard combat cartridges. Thus, the model 100 was made of a kind of barrel extension with an overlying launcher cup. As soon as the bullet passes a gas port in the barrel extension, the gas pressure escapes into the cup and pushes the grenade out. An adjustment screw at the gas port could be used to vary the firing range. Although this system saved another type of ammunition, it was cumbersome in field use. Before fixing the launching cup, the bayonet had to be put on the rifle to give a firm hold to the launcher.

One main problem that arose when the Japanese met the first enemy tanks was the lack of effective ammunition to cope with them. The heavy Type 97 20-mm anti-tank rifle was no longer effective against modern tank armor, and the army did not have any armor-piercing rifle grenades. The development of hollow-charge ammunition was still in its infancy. Early attempts of the Navy with a hollow-charge warhead for torpedoes in the mid-1930s have aroused only little interest and were ignored by the Army.

As part of the mutual exchange of arms technology, in 1942 two German Heereswaffenamt officers were preparing a top secret mission: by direct order of Adolf Hitler, Colonel Paul Niemöller (graduated Dipl.-Ing chemist) and Major Walter Merkel should bring records and patterns of hollow-charge ammunition to Japan. Both men were part of the department Wa.Prüf.1 (ballistic and ammunition department) and were, according to U.S. interrogation records from the period of detention in Japan, already involved in the development of rifle grenades in Germany.

The hollow-charge anti-tank grenade could penetrate 40mm to 80mm or amour steel.

Not much was yet known about this secret mission, but the author has succeeded via long-time recherche in getting in contact with surviving descendants of both men. Unfortunately Colonel Niemöller’s family lost all their belongings during the bombing raids on Berlin, so that only the surviving seaman’s book provides an interesting insight into the secret operations. The descendants of Major Merkel are living in the U.S. today.

The Secret Mission

For reasons of secrecy, both officers were traveling at different times on different ships from Bordeaux in France to Yokohama in Japan. Colonel Niemöller embarked as a paymaster on the blockade runner and auxiliary cruiser “Tannenfels” that left the French harbor on 2 March 1942. Among other things the ship was loaded with machine parts, chemicals and ammunition and fuel to supply the three German auxiliary cruisers “Thor,” “Michel” and “Stier” on the high seas.

Soon after its departure the vessel was detected by a British reconnaissance aircraft. Captain Werner Hase ignored the explicit order of the Navy control center to abort the mission and continued the journey. Fortunately no attack took place. But in the wideness of the Atlantic there would have almost been a catastrophe: for unknown reasons, the stored chemicals in the cargo hold number 2 caught fire. The crew narrowly managed to extinguish the fire before it could spread to the hundreds of drums filled with ether and chloroform in the adjacent cargo hold. The war diary of the Navy later describes the fateful day as follows: “According to a message received from Tokyo, some days after departure from Bordeaux two large fires occurred on the ship and caused a desperate plight. For a while the captain considered the situation as hopeless. With full engagement of officers and crew the attempts to suppress the fire finally succeeded. The captain refers to sabotage as the cause for the fires. […] On board was Colonel Niemöller with an important arms-specific delivery, which was to be handed over to the Japanese Army on order of the Führer.”

Japanese 40mm hollow-charge anti-tank grenade. The Germans later used stems made of Bakelite, but the Japanese never used that material for this purpose.

As if that has not been enough, the ship was caught in a heavy storm in the South Atlantic causing severe damage to the ship’s body and some leaks in the hull. Seriously affected, the “Tannenfels” reached the harbor or Yokohama on 12 May 1942. Eventually Colonel Niemöller was back on firm ground–and was promptly arrested by the harbor police. The reason for this is not clear, and after a few hours he was allowed to leave.

A week later, on 19 May the Japanese Chief of the General Staff Colonel General Sugiyama held a welcome breakfast for Colonel Niemöller. Both Sugiyama and the Vice-Minister of War, Lieutenant General Kimura, thanked Hitler in a letter for sending an “officer on [a] difficult path with valuable material.” In the following time, Colonel Niemöller inter alia met Colonel Kobayashi, an expert on explosives of the Army arsenal No. 2 in Tokyo. Niemöller worked with both the Army and Navy. He was supported by a group of 30 German engineers and chemists who were already in the country and had worked for Japanese companies before the war.

Six weeks after Niemöller’s arrival Major Merkel also reached Yokohama. He had left Bordeaux on 12 December 1942 aboard the blockade runner “Regensburg”. The ship met with the “Dresden” on the high seas, and Merkel changed the vehicle. He arrived in Japan without any incident. The war diary of the Navy says: “Etappen-V Schiff (section support ship) Dresden met on the way from western France to Japan on 31 May 1942 with the Etappen-V Schiff Regensburg and passed over 200 cubic meters of diesel oil from its own storage to the Regensburg. Dresden was then released for Japan and arrived at Yokohama on 22 June 1942 after a successful blockade run. On board was Major Merkel with a second copy of the records that were already brought to Japan by Colonel Niemöller on the Etappen-V Schiff Tannenfels.” The official cargo list of the “Dresden” does not mention any unusual freight.

Disassembled Japanese grenade. The copy was very similarto the German pattern. The stem contains the ignition charge, the percussion fuse and is closed by a base plate.

There was enough to do in Japan. As written in secret reports about the Japanese industry, the German Reich was years ahead in all respects (what a contrast to today). On 11 December 1942 Niemöller sent a telegram to the Army General Staff: “Attempting […] to get something in return. I have doubts because there is little new. I think, as well as the military attaché, that we must be the donor and remain in this role. Strong support of the Japanese is necessary, since they are little inventive on their own. […] The visited companies show little achievement by high labour input. Remarkable is the lack of organizational and inventive talented people.”

Soon after Niemöller’s arrival, the Japanese busily began researching the hollow-charge anti-tank grenades (Gewehr-Panzergranate and Große Gewehr-Panzergranate). An extensive test program was initiated in June 1942 and already in July the first firing test with grenades from their own production was carried out. The German rifle grenade launcher was examined and modified (project “Tate”) and just a month later the production of Japan’s own model started. It was officially introduced as “ni shiki tekidanki” (Type 2). The earliest known launcher is dated August 1942 and was captured by the Americans on 15 October on the Solomon Islands. Also the first grenades from their own mass production were delivered to front troops in August 1942.

Markings on the base plate of the grenade, made by the Army Arsenal No. 1 in Tokyo.

The Rifle Grenade Launcher

In comparing the German rifle grenade launcher with its Japanese copy, the first thing to mention is the much shorter launcher tube. It is just long enough to keep the stem of the Japanese rifle grenade. The distance on which the grenade is forced to rotate is not shorter than on the German standard launcher tube, but even a little longer: The rifling of the tube reaches to the muzzle, while on the German model the last 5mm are smooth.

During the entire production, the Japanese used the same fine thread on the launcher tube, as it was used on the early German model that had been shipped to Japan. The clamp-mount is almost equal to the German model, only the clamps have a different shape corresponding to the Japanese service rifles. Inside the clamps the same mysterious spiral millings as on the early German launchers are present.

Although many Japanese rifle grenade launchers had been captured by the U.S. forces and these devices are also described in the American intelligence reports, it is not known what the launcher sight looked like. If it is mentioned at all, it is usually written that the Japanese sight is probably a copy of the German one, but none had been captured so far. Also in all the Japanese regulations and documents, no sight is described. This fact leads to the conclusion that the Japanese did not use a sight for rifle grenade firing, but aimed on the target by means of auxiliary points on the rifle’s standard rear sight–just as the German soldiers often did, since the launcher sight proved to be very weak in field use.

The officially issued accessories were a canvas carrying bag for 10 grenades with propelling cartridges, a handy wrench and a small canvas pouch for the rifle grenade launcher.

The markings in the first line mean “Type 2 rifle grenade launcher.” The line below shows the symbol of the Nagoya-arsenal and the Japanese year of manufacture “53” (that is 1943).

The Ammunition

For the rifle grenade launcher Type 2 there were only two anti-tank grenades, namely copies of the German early Gewehr-Panzergranate and the advanced Große Gewehr-Panzergranate. Their official Japanese designation translated means “30mm (or 40mm) Type 2 hollow charge rifle grenade.” High-explosive grenades or other types like flare or smoke were not developed.

The design of the rifle grenades corresponds to the German models with some slight variations. It is noteworthy that for the stems only aluminum was used and not Bakelite or other less scarce materials. The base screws have the same cross recess (Phillips) as it was only used on the very early German anti-tank grenades. The grenades were manufactured by two companies: Osaka Army Arsenal and Tokyo Army Arsenal No.1. The explosives for both manufacturers came from the Iju plant of the Tokyo Army Arsenal No. 2.

In order to achieve the best possible precision, all grenades were marked with a stamp consisting of plus and minus signs referring to over- or underweight so the shooter could bear it in mind when aiming on the target. The grenades were packed in simple metal tubes, sealed with cardboard discs.

American reports give data for the 40mm grenade (see chart).

Details of the grenades’ performances can be found in the report “Firing Tests of Japanese Anti-tank Weapons” dated April 1944. During test firing at an M3 Stuart tank the 40mm grenade smoothly penetrated even the 31.8mm thick armor of the turret. When shooting on several armor plates, multi-layered welded together, the grenades penetrated 40mm to 63.5mm. The 30mm grenade proved to be totally inadequate and was not tested any further.

Japanese rifle grenade launcher “ni shiki tekidanki” (Type 2) with opened clamp-mount. Note the large cut-out for the front sight of the Japanese rifles.

Development of a Cluster Bomb

Impressed by the performance of the 40mm hollow-charge grenade, the Japanese used it as a basis for developing a cluster bomb in 1942. There were two different sized containers, a small one for 30 and a large one for 72 cluster bombs. They should make anti-tank fighting from the air more successful, especially as most armored vehicles are less armored on their top side.

The bomb is composed of the body of a standard 40mm grenade, an elongated stem with a 3-fin tail and a sheet metal base plate acting as an air brake. At the height of the tail there is an air wheel attached to the side, which turns out in free fall and unlocks the fuse housed in the stem.

The manufactured bombs differed in some details during the production time. Different lengths of the hollow charge liner are known, from very short to reaching through almost the entire grenade body. Also the air brake metal disk was sometimes replaced by thin struts. On later made bombs the air wheel was put on a 3mm longer axle for a better position in the air stream. No records about the success of the cluster bombs in combat have been found.

On the basis of the rifle grenades it was also experimented with larger grenades in calibers from 57mm to 200mm. By Niemöller’s activity some blueprints of the German Panzerfaust and a wire-guided hollow-charge missile reached Japan. From the latter, the Japanese developed the large hollow-charge bombs “Sakura I” and “Sakura II” (Operation Cherry Blossom) before the war ended. They were to be used in kamikaze missions to sink enemy ships.

After the war, the two German officers were arrested in Tokyo by the Americans and interrogated. After a short time Colonel Niemöller was allowed to leave for Germany. Major Merkel lived in Paris before he returned to Germany in 1963.

The blockade runner and tender “Tannenfels” brought Colonel Niemöller on an adventurous way to Japan. The ship was later sunk on 12 December 1942 in the harbor of Bordeaux by magnetic mines attached to its hull by British frogmen.
Major Walter Merkel was awarded several medals, including the Blockade Runner badge, the War Merit Cross with swords second class and the Japanese Medal of the Rising Sun 4th class.
40MM Grenade Data