From: Iowan in MD/DC
I guess you would have to develop Rangpur, Tezpur and Silchar , so they dont have any max supply draw limits, and then the supply from Calcutta can flow freely through the minor railroad to Silchar and then to Imphal. You could also try shipping supply from Calcutta to Chittagong, stockpile supply there for some time, and once you accumulate a hefty stockpile, disable the stockpiling and let if flow freely through Comilla and Silchar. By dumping supplies in Chittagong you shorten the route the supplies have to travel via railroads and those undeveloped bases.
That's not quite how it works. You really only need to build up the destination base - it can draw supplies from farther "up the chain" than just the next base up.
In order to try the stockpiling method you mention, though, you will have to build up all the bases in order accumulate supplies at any kind of speed.
Honestly, airlifting is faster.