Thread by @JohnAllenGay

Israel has signaled it will respond to Iran's retaliatory strike.

One option they're likely considering: hitting Iran's nuclear program. I coauthored a book in 2013 that studied what a war with Iran would be like, and we dug into this option quite a bit. Here's what to know: 🧵

Iran's nuclear program has several core sites that would be essential to the production of a nuclear weapon. This is an old map but has the core sites: Natanz, Fordow, Arak, and Esfahan (rendered here as Ispahan) (image by Yagasi, CC-BY-SA 4.)

To make a nuclear bomb, you need to take uranium out of the ground, do some chemical processes to make it ready to enrich, enrich it to weapon grade, then turn the weapon grade uranium into a bomb. You also need something to deliver the bomb with.

Esfahan has a uranium conversion facility (UCF) which converts the uranium into uranium hexaflouride, a substance that is much easier to work with for enrichment. This facility is a fairly soft target - it's an industrial plant, you drop a few bombs on it and you're good.

Natanz and Fordow are enrichment plants. They take the uranium hexaflouride in gaseous form and put it in centrifuges that spin the uranium fast enough to separate the isotopes. Take out the isotope you want, and you're enriching.

Here are some Iranian centrifuges at an exhibition - I think their basic IR-1 model. They're precision equipment - the uranium hexaflouride gas is moving through them at extremely high speeds that require everything to be manufactured to high tolerances. You also need a lot of them, since natural uranium is made up of less than 1 percent of the isotope you want, and each step of enrichment only does a bit of purification.

(Photo: Mehr News Agency/Majid Asgaripour, CC BY SA 4.0)

Natanz has two main halls for these things. It's a trickier target than Esfahan. They dug big holes in the ground, built the enrichment halls, then buried them underneath. So you need bombs that can break through that. (More on the weapons later).

Fordow is even harder: they tunneled into a mountain; all you can see on satellite photos is a few entrances. Deep inside the mountain there's a smaller enrichment hall.

Arak is a plutonium reactor. Plutonium is a different pathway to the bomb, one I'm less familiar with, and I've not followed the situation there as closely, so I don't know how high priority a target it would be these days, but it is likely not as difficult to destroy. (Plutonium's main advantage is you don't need as much of it, so you can make the warhead smaller, which is good for putting it on missiles.)

There are some secondary facilities (a research reactor in Tehran and a power reactor in Bushehr [spelled Bouchehr or something French like that on the map above], mines, etc.) But Natanz/Fordow/Arak/Esfahan is what you want to hit if you want to set Iran's nuclear program back.

Israel's air force would be the main actor by far in conducting the attack. You'd have two aircraft as the stars of the show: the F-16I Sufa (left) and the F-15I Ra'am. These are both indigenized derivatives of the American F-16 and F-15E.

(Image: Mathknight, CC BY SA 3.0/Y. A. Fleisher, CC BY-SA 4.0)

These aircraft are both specialized in long range strike. You can see in both pictures they're carrying a lot of big, fat gray fuel tanks and have conformal fuel tanks fitted to the side of their fuselage.

Other aircraft would be acting in a supporting role. Two main ones: Israel's Boeing 707-derived tankers (left) and its F-35I fighters. The 707s provide extra fuel to fighter aircraft, enabling them to get further carrying more and, if needed, burn lots of fuel to do things like fly really fast or engage in dramatic maneuvers, things that become necessary when facing enemy fighters or air defenses. The F-35Is are stealthy - they're invisible, or at least less visible, to enemy radars. They also have advanced electronics and communication systems that can enable them to silently gather information and feed it to other aircraft to act on. Their main limitation is they can't carry as much.
(Image: IDF/CC BY 2.0; IAF, CC BY-SA 4.0)

There would be a lot of other aircraft operating, too. There'd likely be some number of F-15s and F-16s tasked with protecting the strikers, drones to distract air defenses, monitor targets, and assess bomb damage, and radar aircraft to build a picture of the full airspace and guide the strikers in dealing with threats. You might also have aircraft or even helicopters to help rescue downed pilots. But the strikers are the core; everything else is built around them.

The key weapon would be the GBU-28, Israel's highest-end known "bunker buster" bomb. These are huge: they weigh about 5,000 pounds and are almost twenty feet long. The original set of them were built to take out deeply buried Iraqi bunkers in the Persian Gulf War; a bomb that can go deep into the earth and through high-strength concrete needs to be tough, so they were built using leftover artillery barrels. This weapon has been through several iterations. (DOD image)

The huge size of the bombs limits how many the strikers can carry, especially since they're going to be carrying a lot of extra fuel to go to Iran. By my math the best you could likely do is two on an F-15I and maybe 2, probably 1 on an F-16I. Last I checked, the Israelis had 25 F-15Is and I believe about 50 F-16Is. I'm not an IAF specialist but it's also possible they've modified some of their many other F-16s and F-15s with conformal fuel tanks to be capable of making the trip.

Natanz and Fordow are where the limited number of munitions run into potential trouble. Natanz is big, so to be sure you'd want to have bombs hitting throughout the centrifuge halls, and possibly to drop multiple bombs on each aimpoint to really be safe. Working in your favor, explosions are even nastier in confined spaces like a bunker, and again, centrifuges are precision equipment with very complex arrays of piping...and they're loaded with uranium hexaflouride, which is not only radioactive, but also highly toxic.

Fordow is small, so you'd only need a couple of bombs to get into the enrichment hall to do the job. But the problem is getting them in there: they have to plow through who knows how much rock and dirt and concrete. I've seen suggestion that precision guidance could enable a string of bombs to be dropped successively on one aimpoint, tunneling deeper and deeper in, but this seems pretty complex and risky (how much will debris in the "tunnel," for example, hinder successive bombs?). There's also been talk of doing a commando raid on this site, but Israel's ability to do long range, large scale commando insertions is, to my knowledge, much more limited....and these are all highly fortified sites which will now be on maximum alert.

So, you need to drop a lot of bombs and you have a finite number of aircraft that can do that. This is where Iran can make an impact: the margin gets pretty tight if you lose a few aircraft or prevent some munitions from reaching their aimpoints. Given the extreme ranges and loads involved, they might be able to get some aircraft out of the fight simply by heavily engaging them, forcing them to burn speed, altitude, and fuel to survive. Iran's air force is quite weak, but it has decent air defenses and you don't necessarily need to do a lot to be a big problem.

As one Israeli analyst pointed out, though, Israeli aircraft don't have a switch in them that means they can only fly to Iran once. The main insurance policy on this risky attack is doing return rounds. Over time this gets harder on one side of the ledger - your aircrews are worn out and your aircraft need more and more maintenance - and easier on the other - Iran's air defenses get worn down and you update tactics and electronics to address what you've seen so far.

The real question is what the attack accomplishes even if it successfully destroys all the nuclear sites. (There might be unknown nuclear sites, too, although the many high-profile Israeli thefts, assassinations, and sabotage actions against the Iranian nuclear program suggest they have a good picture.)

War is not an engineering problem and it is not a math problem. It aims, as Clausewitz told us, to make the enemy do your will. Destroying his abilities impacts that in the short run, but he can rebuild. It will be harder for Israel to kill the knowledge that underpins the nuclear program. They can and probably will rebuild, meaning we could be replaying this in a few years.

There might be significant disadvantages for the Israelis in future rounds. The Iranians probably wouldn't go around advertising their new nuclear sites (indeed, Natanz and Fordow themselves were originally covert sites), so the Israelis would have to find them.

And Russia and China would have the option of providing new defensive technologies to Iran that could make further attacks harder. Moscow held back for years on providing S-300 anti-aircraft missiles to Tehran, and has much more advanced systems it could provide in the future.

The other constraint on an Israeli attack is volume - they don't have many tankers, and I'm not sure other countries would be eager to help refuel. Attacking the nuclear sites would be a major escalation and could prompt Hezbollah and Iran's proxies and friends in Syria and Iraq to step in, too. That's the scenario in which all this really goes sideways.

There are many other elements of my book I don't cover here - Iran's options to respond, what happens if America gets involved in a big way (we are much more capable but also are easier for Iran to hit thanks to our overextended presence in places like Iraq and eastern Syria), and impacts on things like the oil market.