There is a political battle in Israel, kept below the surface -- as is appropriate when the issue is submarines -- which pits former Defense Minister Moshe Ya'alon against Prime Minister Benjamin ("Bibi") Netanyahu. The battle is over the purchase of new submarines for Israel, bought from Germany under a subsidy.

Israel currently has three Dolphin-class submarines and two Dolphin 2-class submarines (with another on order that will be delivered in 2018). The political argument is over a new purchase of an additional three Dolphin 2+ submarines that probably would replace the original three Dolphins as they are delivered in about a decade.

The latest Dolphin 2-class submarines have 16 multipurpose torpedo tubes: they can fire torpedoes, launch cruise missiles (called SLCMs) and release swimmer delivery systems, such as battery-powered, sub-surface vehicles filled with Israel's equivalent of US Navy SEALS.

Israel has never acknowledged that it has nuclear weapons or nuclear weapons delivery systems. But most analysts and many governments (including the United States) think Israel has at least a few hundred nuclear weapons, some of which are mounted on intermediate-range ballistic missiles (the Jericho II), some that can be carried by aircraft, and still others that are small enough for cruise missiles.

Nuclear deterrence is vital to Israel's long-term survival. Originally intended to counter existential threats from the Soviet Union, Israel's deterrent is now focused on emerging threats, mainly Iran.

Israel has developed a number of different cruise missiles, but allegedly the nuclear-equipped one is the Popeye Turbo. The conventional version is called Hanit Na'a (Nice Spear). The Federation of American Scientists (FAS) revealed in 2002 the Popeye missile was launched from an Israeli submarine off the coast of Sri Lanka in a test that included US observers and led to the American purchase of Popeye missiles that were modified for use on the B-52 bomber. A significant number were purchased from Israel, and Lockheed did the work for the US Air Force.

A submarine-launched missile is generally considered as a second-strike weapon because it has less yield than a missile-launched weapon, shorter range and somewhat lower accuracy, but the great advantage is that the enemy cannot target the submarine in advance, especially a submarine loitering in the water under a silent AIP propulsion system.

All of this is well known in Israel, where the debate is mostly about the budget and how it is allocated between the Air Force, Army and Navy. Overall, Israel's defense budget is already strained by the F-35 acquisition for the Air Force. A decision to buy expensive submarines will reduce modernization resources available to the Army for years to come.

One of the big missing parts in Israel's defense was equipping its armored vehicles -- tanks, infantry fighting vehicles, armored personnel carriers and specialized equipment -- with active defense systems. Israel pioneered the Trophy active defense system produced by Rafael. It is essential today to ward off enemy attacks using Russian and Chinese anti-tank weapons, especially the deadly Kornet anti-tank missile. The Kornet is now in the hands of the Iranians (who are co-producing it), and the weapons have been handed over to Hezbollah.

These are a distinct threat to Israel and to the Israeli army's (IDF) ability to move swiftly against enemy attacks.

Until the second week in November, Israel had not funded acquisition of Trophy for its armored forces. That has now changed, even though Netanyahu won the argument over the submarines.

Underlying the choice of priorities in Israel is the sensitive matter of how soon Iran will acquire a nuclear strike capability. There are differences in how the Israeli intelligence community and Israel's prime minister assess the overall risk. Israeli intelligence does not think the Iranians are yet in a position to threaten Israel, even though they have long-range ballistic missiles. They also tend to think (as does the CIA) that the restraints imposed by the nuclear deal led by the United States will delay Iran's deployment of nuclear weapons for at least ten years.

But even if they're right, Israel needs to be prepared for the end of that decade – when Iran can openly flout nuclear weapons without in any way violating the nuclear deal.

President-elect Trump says he will scuttle the nuclear deal with Iran. This he should do, but with or without a nuclear deal with Iran, Israel has to be prepared.

Netanyahu's decision, from any angle, is realistic and responsible. Israel will get new submarines.

Stephen Bryen was founder and first head of the Defense Technology Security Administration. He also worked in industry as the president of Finmeccanica North America and as president of SDB Partners LLC.