SH5 is its own game, unrelated (well... sort of) to SH4. SH4 is Pacific Theatre of Operations, originally only with US Fleetboats, and SH5 took the game back to the Atlantic Theatre of Operations, as German U-Boats, with a re-worked UI... I ~still~ can't get up and down ladders in that game... sigh
SH4 v1.5 is the latest / greatest update for "Silent Hunter: Wolves of the Pacific", aka: "Silent Hunter 4:Wolves of the Pacific". If you have your install updated to v1.4, that is the last of the free updates that Ubisoft offered. The v1.5 update has the Uboat Missions Add-On. They rolled that into the "Gold Edition - Silent Hunter: Wolves of the Pacific" release shortly after.
Some of the mods that work on v1.4 are available here, including Fall of the Rising Sun v2.0 (NOT the Ultimate Edition), which is in German only. You might be able to dig up TMO v1.6 (1.6.7?), and some of Websters mods work in v1.4, but most others would be unavailable here. One place you could look would be
NexusMods, but about all they have are old versions of mods. They did "capture" some of the old FileFront stuff, but not all of it, and some of the mods they have do not have all of the parts. They leave it up to the user to determine suitability for their use...