When playing Global or Pacific 1940, I typically use the British to try and stop the Japanese on the Asian mainland while using Anzac and the US to confront the Japanese fleet and push them out of the Pacific.
It sounds like the guy that you are playing against is using an all out “India Crush” strategy to knock you out Calcutta in the early game. While it can be hard to defend against a really determined Japanese player, there are things that you can do to prevent this or at the very least make the Japanese losses severe.
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Build Troops - This will give you the best defense value for your money. If he is hitting you on turn 4, then you can have about 25 units (approx) on India when he attacks
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Buy an AA gun on the first turn - While some people may disagree with me on this buy, I think that it is a must for the UK Pacific. If the Japanese are bringing in 15 planes or so to knock out India, chance are you will destroy at least 2 maby 3 planes. Even if they do not go for the India crush, I say that having that AA gun in your main stack is huge for offsetting the Japanese air advantage.
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Block with your fleet - Send out the transport to take what DEI islands that you can early on, but save the other ships to block the Japanese navy from sending transports into India (which I assume they are doing). If you can save yourself just one turn this way, that is another 7-8 inf that you can put in India.