Israel has purchased two Dolphin-class, "nuclear-capable" submarines from Germany, the Jerusalem Post reported this week. German officials say the subs are "designed for the conduct of conventional war," but critics of the deal say they're equipped to carry nuclear weapons. What makes these submarines nuclear-capable?
The size of their torpedo tubes. Nonproliferation experts call the Dolphin-class German subs "nuclear-capable" because they come with torpedo tubes in two diameters—533 mm and 650 mm. For conventional warfare, the Israelis might do fine with just the 533 mm tubes, which can fire off regular missiles like the American-supplied Harpoon. The presence of the larger tubes suggests that Israel might be planning to install long-range nuclear cruise missiles that they may have developed in-house.
Meanwhile, Germany says it's delivering the subs with liners inserted into the big tubes, which brings them down from 650 mm to 533 mm. The liners won't make the subs any less nuclear-capable, though: If the Israelis wanted to use the bigger tubes, they could just pull the liners out. They might also use the smaller tubes to fire off nuked-up versions of the Harpoon missiles. (Unconfirmed reports suggest that Israel has developed nuclear-armed, underwater missiles in both sizes.)
For the Israelis, the 650 mm missiles would be preferable, since they would have a much longer range and would allow nuclear-armed subs based in the Mediterranean to strike directly at Iran. In theory, such missiles would give Israel a strong "second-strike capability" in the event of an Iranian attack. (Even if Iran blew up all the nuclear missiles in Israel proper, the subs could still launch a counterattack.)
Whether these Dolphin-class subs are nuclear-capable depends only on what sorts of nuclear missiles Israel has in its arsenal. In theory, any military submarine can fire off a nuclear weapon as long as that weapon fits in its torpedo tubes or can be launched from it in some other way. Some early American nuclear subs lumbered around with big, hangarlike structures bolted to their backsides. The hangars opened up to fire off gigantic cruise missiles.
Bonus Explainer: Is a "nuclear-powered" submarine the same thing as a "nuclear-capable" submarine? No. Nuclear-powered subs use reactors to generate the energy that other subs get from diesel engines. This gives them at least one major advantage: They can stay submerged indefinitely, or at least until the crew runs out of food. That makes nuclear-powered subs a good choice for nuclear armament, since they can stay underwater and out of harm's way in the event of a war. (Not all nuclear-powered submarines are nuclear-armed, and vice-versa.)
Standard submarines must surface for air on a regular basis, so the diesel engines can run and recharge the batteries that are used underwater. The diesel-electric submarines that Israel just bought from Germany make use of a new technology called "air-independent propulsion," which allows them to stay submerged for weeks instead of days.
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Explainer thanks Andrew Karam of MJW Corporation, Clay Moltz of the Monterey Institute, and John Pike of GlobalSecurity.org.