The save system in SH4 is pretty buggy. I've found that if I do new saves for each mission with no overwrites then the save-related CTDs are kept to a minimum. I've had to purge all savegames before to fix CTD issues .. but I keep the purged files so that there's a chance I can hack together a fix - as happened recently when crew injuries from a patrol were causing the next patrol to CTD when launching.
If I'm ever offered a new conning tower, I hope I get the option to keep my old one ..
*edit* The furthest I've played through to in OM is to the end of 1941. I tend to get sunk by bugs.
