I've always wondered - why did these two countries not co-operate more closely during the war? I know that the 'Pact of Steel' was more a marriage of convenience between three fascist dictatorships that arose with similar motives and agendas moreso than an actual plan of solidarity and alliance; but still, it would have made more sense whilst engaged in the war to exchange information and ideas more than they historically did.
Imagine, for example, the Japanese sending the German's plans for the Zero? A plane capable of escorting bombers to and from the target, with German cannon (the Japanese cannon were a poor copy of the Oerlikon), a few European modifications (self-sealing tanks, pilot armour), and it would have given the German's an aircraft that could have taken on the Spitfire on it's own terms (manoevrability on the horizontal plane) whilst still having a plane that was incomparable (in the early war) in the vertical plane. With fuel injection, the Me109 pilot could push the stick forward, and therefore could dive into negative-g without the engine cutting out, as happened to gravity-fed carburettors in British aircraft.
Even this is only one of myriad things that could have made the alliance actually mean something - it just seems to me to have been such a missed opportunity. Anyone else agree?