There was generally next to no functional military cooperation between the Japanese and the Germans during the war. There were technical exchanges, trade, and a German group of U-boats that operated out of Penang (the Monsun Gruppe ), but that was about the limit of Axis cooperation. The sheer geographic separation as well as the differing strategic priorities of each Axis partner rendered the alliance dysfunctional at the best of times.

The Japanese inaction against Siberia throughout the war was a case in point. The IJA had already fought two sharp border conflicts with the Soviets in 1938 and 1939 which showed the shortcomings of the IJA as a modern force. The swift fall of France in 1940 further underscored to the IJN the need to modernize its forces. The problem the existing Japanese empire did not possess the resources needed for such a modernization. This led the IJA to adapt elements of the IJN's Nanshin (southern drive) to seize the resources of Southeast Asia for modernization as well as cut of the KMT from Western supplies. Ironically, while planning for Barbarossa, Germany's Japanese policy encouraged this reorientation with the logic that Japan occupying these areas would deny them to the UK and entangle American naval power in the Pacific. Tokyo was largely kept in the dark about the Soviet invasion despite the Tripartite Pact. Although Barbarossa did encourage some hotheads in the Kwantung Army to propose a Siberian attack, cooler heads in the IJA's General Staff prevail because there were significant doubts that Japan had the capability to invade and hold Soviet territory without the Southern Resources Area (the term for SEA among both services). Germany's push for a Japanese Siberian invasion only picked up steam after Barbarossa had stalled, by which time the die had been cast for the Nanshin. Although some in the IJA conceived of a later invasion of Siberia once the Pacific War had been won, the war proved a bottomless sink of men and material that prevented any expansion northward, and all plans for a Soviet war became postponed indefinitely.

The trading relationship between the Axis partners also showed a similar pattern of short-sighted policies and different priorities. For the most part, technology and trade in raw materials between Germany and Japan occurred through individual blockade-runners. In exchange for examples of German military technology and plans, the Japanese provided raw materials and other items the Allied blockade prevented from being imported to Germany. From the outbreak of the war to around 1942, surface ships formed the bulk of inter-Axis trade. Of some 104,232 tons of raw materials shipped from East Asia to Europe in 1941-42, approximately 75,000 tons arrived in European ports. The Germans and their Italian allies did not make the most of this brief lifeline and the items ordered from Japan included non-essential materials like tea and coffee and cooking oils. Although these raw material helped ease domestic shortages, it exemplified the skewed and myopic priorities of Italy and Germany. The nature of industrial warfare necessitated a more ruthless prioritization, especially given the acute shortages of strategic materials like rubber and tungsten. This short-sightedness came to a fore by 1942 when Allied naval superiority was able to cut the surface blockade-running lines with ease. Although there were tentative steps towards an aerial connection between East Asia and Europe, the only practical option for the Axis to run the blockade was submarines. German Type IX U-boats could carry at best 2-3% of the tonnage of a surface blockade-runner and the larger Japanese submarines were only slightly better. The inability of the European Axis to prioritize their brief window of opportunity in 1941-42 of building up stockpiles of East Asian raw materials led to persistent shortfalls of these materials in the German war economy and their substitution by inferior ersatz ones.

Payment for this exchange was a source of consistent tension within the alliance. The Japanese would pay for German plans and examples of technical equipment with raw materials supplemented by gold, but the Germans would seldom agree on the Japanese exchange ratio for these goods. The disagreement over payment and equitable exchange spilled over into operational matters. The Kriegsmarine ordered the commanders of the Monsun Gruppe of U-boats based in Malaysia to hide the existence of the newly-developed acoustic T-5 homing torpedo from their Japanese hosts or give them an explanation of its technical workings. German industrial firms also expressed grave reservations about handing over plans and other industrial information without first getting guarantees of honoring German patents. There were a few notable instances of fruitful collaboration, such as in 1943 when Luftwaffe general Erhard Milch circumvented the Kriegsmarine and approached the IJN attache Abe Katsuo if the IJN could ship tungsten in exchange for plans for radio-controlled bombs and examples of Luftwaffe autocannon. The IJN agreed to this transfer and the submarine I-29 delivered the tungsten to Lorient in March 1944 and Milch provided the equipment as payment in kind without hassling over the exchange ratio.

But this type of cooperation was the exception rather than the rule and the inter-Axis trade relationship was characterized by mutual distrust, skewed priorities, interagency rivalries, and miscommunications.

Sources

Barnhart, Michael A. Japan Prepares for Total War: The Search for Economic Security, 1919-1941. Ithaca: Cornell University Press, 1987.

Krug, Hans-Joachim. Reluctant Allies: German-Japanese Naval Relations in World War II. Annapolis, Md: Naval Institute Press, 2001.

Militärgeschichtliches Forschungsamt. Germany and the Second World War Volume VI, The global war: widening of the conflict into a world war and the shift of the Iniative 1941-1943 Oxford: Clarendon Press, 2001.