Time compression is for noobs. No time speed acceleration.
Only hardcore, only 1 (real time) x 1 (in-game time).
UPD: And last problem - Flotillas.upc need to add blocks for XXI type submarine: since each sub type has it's own missions/objects (check inside file), create your own missions for XXI or take II/VII missions and replace them for XXI.
But main is that you can ride XXI type in 1939 and game will not crash in loading process.
Maybe some kind understanding person will make MOD for us.