If all your really interested in is a uboat campaign, then id do as Jimbuna suggested and load SH3 with GWX, or any other supermod that happens to grab your attention.
SH5 has a long way to go. I'm sorta playing it now because its new to me still, and some things i really like despite many functional shortcomings.
SH4, really does get a bad and undeserved rap. In reality, its two submarine sims rolled into one, and you have many choices available as to what type of submarine you want to drive and areas of operation. Admittidly though, SH4, is a bit of a mixed bag where functionality is concerned, but many of the shortcomings have been addressed in some manner.
SH5 has in some ways left me yearing for a good type9 uboat game and had me contemplating starting a new supermod for SH4 for JUST that expressed purpose since its totally lacking in SH5, but ahh... i just don't have any wind in my sails. Easier to point to Operation Monson, and Lurkers excellent work, that, and if i really wanted long range patrols, id rather have 6 tubes forward and 4 aft
