RE sub types.
The sub types in SH4 are the ones used in the pacfic theater, however, they represent an evolution in design. Not all commands being offered are "upgrades".
Progressivly you could say, in order of evolution:
S class -> Porpoise -> Salmon -> Sargo -> Tambor-> Gar-> Gato-> Balao
This is a pretty good thread on it :
"An overview of U.S Subs used in SH4"
http://forums.ubi.com/eve/forums/a/t...1941046945/p/1