[peterloo]

I think that the above replies have already answered the question... But to make it historical accurate, a 1945 start is necessary...

modders will do their job... No worry

But year 1945 won't be great fun... no more mechants travel from Phillipines to Japan... But there are reinforcements from Japan to Iwo Jima, Okiawa. There is also Operation Ten-Go, the journey of Yamato to the eternity.

Probably there will be pilot rescuring mission (bombers => firebomb Japan)
Tons of sucidal boats / kamikaze planes to deal with
Spying Japanese bases missions
Mining Japanese waters (if there is mining function included)