If I recall correctly, it one of the following 2: NSS_UboatXX.val or NSS_UboatXX.sim
In SH3 1.4B there was no problem with going at less than 2 kts, subs had neutral buoyancy, but I think it was altered by GWX and probably by NYGM too. Those are my 2 cents...
Sorry I can't help you more, my knowledge of those issues is very limited
CapZap