[magic452]

Clay my good friend, you already have a copy of Silent Hunter IV Gold Edition.
G2B sent you one in 2010

That is as BernieP2 said is Silent Hunter IV (4) Version 1.5.
It plays US Fleetboats same as your V1.4 only it fixes some problems and adds some new features. It also adds a U Boat campaign to the game but you do not have to play U Boats, it's like a separate game.

Uninstall SH4 V1.4 and reinstall from the Gold Edition disk SHIV V1.5.

On the game menu screen you'll see the same things you see in V1.4 plus there is a U Boat missions option. Just don't click that and you will be playing the same SH4 you are playing today. Don't add any mods or anything just take a boat out and see how the game plays.
You can mod it later and we can help you better as you will be playing the same game almost ever body else is.

Very few here play V 1.4 and all the new mods are for SHIV V1.5, TMO, RFB, RSRD and FOTRS are US Fleetboat mods they have nothing to do with U Boats.

SH 5 is some entirely different and I'm sure you are not interested in it as it is only U Boats.

You have put a lot of time and effort into this and I would love to see you get to play it. Just take things one small step at a time and I'm sure you'll get it going.

Magic