688i was the original game and as such, later versions improved over it. I did not find any difficulties adapting from 688i to SC and then to DW when playing with the Los Angeles submarine, because stations and functionality of interface are virtually the same. If you stick to the good old LA nuke, you will see that differences come out mainly in sensors and AI refinements. There are some major changes in those, but nothing you can't adapt well to. For example, in 688i the broadband was the place to look for new contacts, while in SC and DW it more accurately is the narrow band, etc.
I wouldn't be afraid of DW, if you stick to one platform it can be easy to master soon, and the scalable difficulty level is always a nice help....anything you find too complicated at first, just let the auto crew do it
If you are planning to progressively go from one to the next, then my advice would be to stick to the 688i for starters.
Also, remember that all three games have a bunch of info in the form of player written tutorials, and as such the best description and help for each game will be:
For 688i = The Bluebook of tactics
For SC = TimmyG's SCHQ TACMAN REV2
For DW = Landlubber's guide and the various specific platform guides (TLAM's Kilo guide, Mahuja's Frigate guide, Oneshot's Orion guide, etc...)
In any case, for the later titles the earlier manuals always have good info and some use. So I would recommend to get them either here at subsim.com downloads section or at Bill Nichol's site
www.subguru.com
Happy hunting
