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Wars are unpredictable. Even the Israelis and the Iranians cannot know how their current conflict will end.

However, there are several comparisons to be made. First, consider the six-day war of 1967. Second, think about the Iraq war of 2003. A third possibility is a new form of conflict where Iran might use unconventional tactics to retaliate against Israel and the West. This could escalate into a hybrid war, possibly involving terrorism or even weapons of mass destruction.

The Netanyahu administration hopes for a repeat of the 1967 scenario, where Israel’s pre-emptive strike effectively dismantled the Egyptian air force on the ground, leading to a swift victory over Egypt, Syria, and Jordan.

Israel has indeed achieved rapid and remarkable initial successes in the current conflict. However, dismantling Iran’s widely spread and mostly underground nuclear program presents a far more complex challenge than eliminating surface-level targets.

Some critics, particularly in the US, fear that as a result we are witnessing a rerun of the early stages of the 2003 Iraq war. That, too, was supposedly fought to prevent nuclear proliferation, with the background ambition of bringing about regime change. After initial success for the US-led coalition, it turned into a bloody quagmire.

It is most likely, however, that the Israel-Iran war will follow its own distinct path. One scenario that worries western security officials involves a desperate Iranian regime deciding to strike back through unconventional means.

As one senior policymaker puts it: “The reason this has not yet turned into world war three, is that Iran seems to have very limited means to strike back conventionally.” Another senior official says there may also be limitations on the Israeli government’s ability to keep fighting at this intensity because its country has limited “magazine depth” (weapons stockpiles, in non-jargon).

If the Iranian regime believes that, nonetheless, it is going down to a bad defeat in a conventional conflict, it would have a difficult choice. It could meekly accept the situation and try to negotiate its way out of trouble. Or it could escalate by unconventional means. That threshold is more likely to be crossed if the regime believes it is in a battle for survival and needs to demonstrate its strength to the Iranian people and the world. Rage and the desire for vengeance should also not be underestimated.

In Washington and Brussels there are concerns that if the Iranian regime is cornered it might lash out in desperation.

In the recent past, the US has accused Iran of having covert biological and chemical weapons programmes. If those fears are correct, Tehran may have the means of striking back at Israeli or American targets in a deadly but deniable fashion.

The International Atomic Energy Agency has also stated that Iran has a considerable stockpile of uranium that is enriched to 60 per cent. It is generally believed that Tehran would need to get to 90 per cent enrichment to make a nuclear weapon. This could be done within days — although weaponisation would take much longer.

However, weapons experts point out that it is actually possible to fashion a crude nuclear weapon with uranium enriched to 60 per cent. David Albright and Sarah Burkhard, of the Institute for Science and International Security think-tank, write that “an enrichment level of 60 per cent suffices to create a relatively compact nuclear explosive; further enrichment to 80 or 90 per cent is not needed”. That kind of weapon would be suitable for “delivery by a crude delivery system such as an aircraft, shipping container, or truck, sufficient to establish Iran as a nuclear power”.

Iran could choose to demonstrate a crude nuclear weapon to try to shock Israel into ending the war. Another possibility is that it could actually set off a “dirty bomb” — which uses conventional explosives to scatter radioactive material. The kind of scenario that experts worry about would be the use of a ship to detonate a device near the Israeli port of Haifa.

These are the considerations that are being weighed — not just by Israel but by the US. It is generally believed that only America has bombs powerful enough to have a chance of destroying Iran’s underground nuclear facility at Fordow.

There are many in Washington who believe (or fear) that the US will join a second stage of the bombing campaign, in an effort to destroy Fordow and finish off Iran’s nuclear weapons programme. But there would be no guarantee that even an American-led attack on Fordow could achieve that. Ehud Barak, the former prime minister of Israel, writes: “The truth is, even the Americans cannot delay Iran’s arrival at nuclear weapons by more than a few months.”

Barak argues the only way to guarantee that Iran never goes nuclear is for the US and Israel “to declare war against the regime itself until it is brought down”.

But Donald Trump has repeatedly pledged to be a peacemaker and has called on Iran and Israel to make a deal. Just last month, he gave a landmark speech in Riyadh in which he scorned the idea that outsiders can bring positive change to the Middle East through force. It would be a supreme irony — and a terrible policy failure — if Trump found himself dragged into another war for regime change in the Middle East.

gideon.rachman@ft.com