Look at the menu_1024_768.ini file sometime, and in SH4, there are sections devoted to SH3. My guess is since the game loads everything in the game folder, that it is difficult to part company with a file named in the menu_1024_768.ini file, and editing that is a bit tough, even if you use the SH5 editor. Kind of like a house of cards, in that one section holds up and supports the next. Speaking of which, the SH5 version of the menu_1024_768.ini has SH3 "calls" also, along with SH4 leftovers... There is a reason, whatever it is, that they left those there. One thing to notice is that the US Fleetboat bears a striking resemblance to a Type IXD2... There's a reason these game companies went to the DVD-R format instead of 1.44mb floppies...
