The two new Dolphins will cost about $650 million each, with Germany picking up a third of the coast, as part of their reparations for World War II atrocities against Jews. The Dolphins have an fuel cell based propulsion system which enable them to stay under waters for over a week at a time. The Dolphins are also very quiet, and very difficult for the Iranians to hunt down and destroy. The first three Dolphins don't have the AIP (Air Independent Propulsion) system.
Israel equipped it's new Dolphin class submarines with nuclear cruise missiles in 2002. Israel also fitted their 135 kilometer range Harpoon missiles with nuclear warheads. These missiles are fired from the subs torpedo tubes. The 1,625 ton Dolphins can carry 16 torpedoes or missiles and have ten forward torpedo tubes (four of them the larger 650mm -26 inch- size). The Dolphins are considered the most modern non-nuclear subs in the world. The first three and cost $320 million each. They have a crew of 35 and can dive to a depth of more than 600 feet.
The Israelis have developed a cruise missile, which is has a range of 1,500 kilometers and carries a 200 kiloton nuclear warhead. The objective of deploying nukes on subs is to further enhance deterrence to any nation launching a nuclear strike against Israel. If one of the Dolphins are always at sea, even a first strike against Israel would not prevent a nuclear strike by submarine launched nukes. Israel is reported to be trying to set up a base in the Red Sea, because the two most likely nuclear attackers are Iraq and Iran.
The Israeli government admitted that they had finally, after over two years of negotiations, signed a deal with Germany to receive two more Dolphin class submarines. It appears that Israel will receive two that are already built, or under construction. Israel already has three Dolphins, which they received 5-6 years ago. These are now being upgraded by a team of German engineers. The upgrades include larger fuel capacity, converting more torpedo tubes to the larger 650mm size, and installing new electronics. The fuel and torpedo tube mods appear to have something to do with stationing the subs off the coast of Iran. Larger torpedo tubes allow the subs to carry longer range missiles. The larger fuel capacity makes it easier to move Dolphins from the Mediterranean to the Indian ocean. Although Israel has a naval base on the Red Sea, Egypt will not allow Israeli subs to use the Suez canal. So the Dolphins have to go around Africa. Currently, that is apparently being accomplished via a refueling stop in Eritrea. But if that access is denied in the future, the larger fuel capacity will enable the Dolphins to make it all the way on their own. Larger fuel capacity also allows the subs to spend more time on station off the Iranian coast. Currently the Dolphins can stay at sea for about 40 days (moving at about 14 kilometers an hour, on the surface, for up to 8,000 kilometers). Larger fuel capacity could extend range to over 10,000 kilometers, and endurance to about 50 days.