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My POD is that von Ribbentrop became German Foreign Minister in 1936 and immediately persuaded Hitler that giving technology to Japan was in Germany's interest because it would make Japan stronger and more aggressive which would distract America, Britain, France and the USSR from opposing Germany. The only conditions were that the absence of payment should be kept secret, nothing should be passed to other countries and that details should not be transmitted by radio (because Germany was worried that codes could be broken). Naturally, Germany requested that Japan give them access to some Japanese discoveries but trusted them to show fairness (yes that really is ASB).

Examples of the sort of information transfered before September 1939 might include the 88 mm Flak 36, German welding techniques and armour compositions, the DB 601 aero-engine, radars (Seetakt, Freya and Wurzburg), hydrophones and sonar, aircraft radios and the Ju-88 design. Japan was interested in some of these as a German 88 mm supplied to China was captured and reverse engineered. Also the DB-601 was produced in Japan but the fuel injection system was never supplied and the metallurgy was not copied causing bearing failures.

We could imagine air dropped torpedoes and the cavity magnetron coming to Germany. If collaboration took off, we could imagine a Bf-109 unit demonstrating energy tactics in Japan in summer 1939 in return for the pilots for Graf Zeppelin being trained to land on Kaga and Soryu.

Would any of this produce interesting consequences? Are there other suggestions for technologies to exchange?
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