Their no-denial-no-confirm policy comes from the 60's, before Iran was the enemy. When was the leak? 

Also, the US did an interesting experiment: they paid (well) two physics professors, competent but with no nuclear physics experience, to stop whatever they were doing and design a A-bomb using only public info. In two years, they had a functional design on paper, missing only workable engineering details.  So, if Israel is unable to build A-bombs, it must be due to lack of will, $, or industrial capacity, and not lack of knowledge.

And keeping subs on the sea with no nuclear missiles would be an expensive way to bluff. 

But who knows?