Israel has signed a contract with Germany for a sixth Dolphin-class submarine capable of being outfitted with nuclear-tipped cruise missiles, according to the Jerusalem Post.

The Israeli Navy already fields three operational Dolphin subs.  Another two are scheduled for delivery later this year. A sixth one will help strengthen Israel's nuclear deterrent vis a vis Iran. 

In strategic-arms parlance, this gives Israel a second-strike capability.  The  Dolphin subs effectively would be immune to a first-strike Iranian attack, leaving them available for nuclear retaliation.   Theoretically, the German subs thus might stay the mullahs' hands from assured atomic devastation of their own country.

Nuclear deterrence worked during the Cold War, when Washington and Moscow faced mutual assured destruction (MAD) should either have contemplated a first-strike nuclear attack on the other.  But would it work this time with theocratic, fanatical zealots with their fingers on Iran's nuclear buttons?

During the Cold War, neither side wanted to annihilate the other.  This time, however, Iranian leaders deem elimination of the Jewish state an overriding objective.  As Ali Rafsanjani, a former president of Iran and head of a powerful mullahs' oversight panel, famously remarked: One Iranian nuke would be sufficient to destroy Israel, with minimal collateral damage to Muslims.

The bottom line is that nobody knows for sure if nuclear deterrence would work again. Which is why preventing Iran from becoming a nuclear power is the pre-eminent moral imperative of our age. An exchange of nuclear attacks would be a global catastrophe affecting all of mankind.

In the meantime, Israel is prepared for any and all existential threats - acting where feasible in concert with the international community but, if necessary, on its own.  Its growing Dolphin fleet is a timely reminder of what's at stake.  Containment might not work the second time around.

Leo Rennert is a former White House correspondent and Washington bureau chief of McClatchy Newspapers