If you have a Steam version of the game, you'll have to purchase the
Silent Hunter 4 Uboat Missions Add-on (US Store link), which is another $10 currently, but does go "on sale" every once in a while. Unfortunately, you cannot use the Ubisoft v1.4 patch on a Steam version of the game.
If you have a disk version of the game, or something like an Amazon download, then you can use the
Ubisoft SH4 v1.4 patch (SubSim download link) to update to that in-between version. I do not remember though, if that gets rid of the repeat missions. What can happen, even with the repeats removed, as jimmbbo encountered, is you might be in a SubRon that has more SpecOps missions than others, so you might be assigned a few in a row, but they shouldn't be repeats.
It is recommended though that you get your install updated to v1.5 however you can. Most of the mods are for v1.5, and it is the version with the least amount of trouble in Stock trim. Version 1.3 can be very frustrating.
