I was under the impression that the Israelis already had a sea based quasi deterent force in the form of the existing dolphins with Popeye Turbo missiles?

They have been developing this, but it’s no good on subs that need to Snort every second day. With the two new subs and their AIP system, they can go six weeks before ever having to surface again, this will keep the Iranian Navy guessing as to where they are. Add to this, how conjested the Gulf is these days and you can see already what a master plan this is.