Pontiouspilot and desicat - You guys bring up some good points. I'll try to address a few of them.
First, it is possible to take Bombay. It is also possible to take Karachi. The challenge is taking both. I don't think it's been done before in PBEM, and as I see it, here's why:
If Japan goes for Bombay first, they have two choices:
1. Land right on the hex and try to take it before the Allies have time to rail in additional reinforcements. Since Bombay is heavy urban terrain, its defenders get a huge combat bonus even with no fort levels. For this reason, trying to take it quickly makes a lot of sense because if you don't take it quickly, the odds are good that you never take it at all. Once the Allies get 1000+ AV into Bombay, it becomes almost impossible to capture. (See the recent efforts of Mr Kane and njp72, both good Japanese players who tried but failed to take Bombay.) The problem with landing directly at Bombay is that it has both mines and 6" CD guns. If Japan lands here, whatever the structure of the invasion, they will take losses. (Lost transports, lost escorts, lost troops, considerable disruption on landing, damaged BBs and CAs, etc. Not ideal for auto-victory giving all those points away.)
2. Land at bases either north or south (or both) of Bombay, then try to rapidly close off the railway lines into the city before reinforcements can be sent in. This way Japan avoids the inevitable losses a landing directly at Bombay would suffer, but pays for it with lost time. (If the rails are not closed quickly enough, extra Allied AV will arrive by train and Bombay may never fall. Even if the rails into Bombay are closed down, the Allies will have plenty of time to rail reinforcements into Karachi instead, making that city almost impossible to take.
If Japan goes for Karachi first, they face essentially the same choice, except that if they elect not to land directly in Karachi, there aren't any good alternative bases nearby. It'll take a long while just to get troops to the city, nevermind actually capturing it. Karachi also triggers automatic reinforcements (one divison of which shows up right in Karachi itself, making things even more difficult.)
Opt for Bombay first, you don't trigger emergency reinforcements, but you do give the Allies time to rail in reinforcements to Karachi.
Opt for Karachi first, you do trigger reinforcements, but most of them will be stuck in Aden for the rest of '42 if your attack succeeds and you take the city (along with Socotra.) Along with triggering the reinforcements though, you also give the Allies time to rail in reinforcements into Bombay...
Taking them both at the same time would seem to be the ideal solution, except that even in Scenario 2 I don't think Japan has quite enough to pull this off.
As to being forced to commit to India in order to maintain the chance for auto-victory - desicat is correct, that's really not the case. If Japan were to stop advancing right now, and instead just consolidated everywhere (meaning finishing with Java and the Phillipines, but conquering nothing else outside of China) they would still be right on the verge of a 4-1 victory point advantage when all was said and done. (It would end up roughly 19,000 Japanese VPs against 5,000 Allied VPs as things stand now.) Since Japan doesn't really need to completely stop expansion yet (remember it's still only January 1942) it may still be possible to pick up enough points elsewhere on the map, India or no, to tip the scales.
Lastly, to pontiouspilots' point about Ceylon: Yes - owning Ceylon, along with Diego Garcia, Addu, the Cocos, etc., and having months to turn them into defensible positions should make any advance against Japan on this side of the map very difficult. As Japan you only have one weapon (the KB) which can completely assure the stability of any given flank, so it defintely helps to have one or two fewer flanks. For that reason alone I think Ceylon is worth the effort, even if Japan doesn't plan any further advances in the IO.
< Message edited by Quixote -- 9/6/2013 2:32:31 PM >