My newest Japan strategy. Do you worry about your fleet getting out of position trying to sack Calcutta? This strategy has almost your entire fleet back in SZ 6 end of J2 and Calcutta falls J6. (Or you can annihilate the Serbian army and then sack Calcutta turn 9)
https://www.youtube.com/playlist?list=PLC5zN4iV9YdEH0yGwdDM36i0QUevTcNa6