At this time, the best deal is from Ubisoft themselves, at least on the US store:
https://store.ubi.com/us/silent-hunt...tml?lang=en_US
They have SH3 for the same price, and SH2 for a buck less. SH5 is at its regular $9.99 price
On Steam, they have the Silent Hunter Package:
https://store.steampowered.com/sub/13751/
but no SHII... and alas, no Destroyer Command at either, to go with the SHII... sigh
If doing the Steam version, you need to have the Steam Silent Hunter Wolves of the Pacific (which is v1.3), ~AND~ the U-Boat Mission Add-on to have SH4 v1.5. You cannot apply the Ubisoft v1.4 patch to the Steam WotP, and you cannot apply the Steam Uboat Missions Addon to any other copy of the game, only a Steam copy - at least, that's the way it used to be...