Israel just did something a wee bit nutty with their most recent wish list of US war goodies. It's one of those nerdtastically insider geek things that might actually mean some really interesting stuff.

So — drumroll please — reports have just emerged that Israel wants to buy a proposed, but as yet unmade, version of the F-15 fighter jet called the F-15SE Silent Eagle, in addition to several F-35s.

Okay, so it's not that exciting, unless you've been following the Israeli Air Force. But if you have, this purchase tells you something interesting about what advice those guys are getting from their strategic-planning Ouija boards on the topic of stealth.

To understand why this matters, let's roll the flashback reel. Right now, the Israeli Air Force flies a sizable fleet of US-made F-15 and F-16 aircraft (in various configurations). They've proven to be good, solid aircraft. (In 1983, an Israeli pilot was able to bring his F-15D back home after losing a wing in a mid-air collision. Yes, you read that right: a wing.) In technological terms, they're "fourth generation" or 4th gen jets, meaning they first came into service during the 1970s and have things like computers, advanced avionics, and other such stuff that their third generation predecessors lacked.

So how do you level up from there? While there's no complete and universally agreed-upon list of everything that makes fifth-generation aircraft legit 5th gen, there is one inescapable requirement: that the plane be designed from the ground up as a stealth aircraft.

There are a lot of things that go into making an aircraft stealthy, but making an aircraft truly stealthy basically means baking stealth features into the design from day one. Mostly, this is because a huge part of stealth is about geometry, and if being the stealthiest jet in Stealth Town is your objective, you have to make some pretty complex aerodynamic and performance trades. While it's possible to do a whole lot of aftermarket stuff to a jet to make it stealthier, without incorporating those design features from the start, you'll always end up being a bit easier to spot on radar than a true 5th gen aircraft. After-market stealth bling will, to some extent, always be a matter of putting lipstick on a pig.

Which brings us to the notion of 4.5 gen (or 4+ gen) jets, which are, as the name would suggest, more advanced than 4th gen, but not full-on 5th gen aircraft. Some of these 4.5 gen jets are older 4th gen aircraft designs with aftermarket stealthification. Others skip the stealth stuff altogether and just incorporate all the super sweet, top-end electronic sensor-fusion gear of a 5th gen fighter without doing that clean-sheet all-stealth design stuff. But the one thing that is clear is that they're more advanced than 4th gen and less advanced than 5th gen aircraft.

The F-15SE, or Silent Eagle, that Israel is looking to buy is a pretty classic 4.5 gen design. The basic F-15 first flew in 1972, but this version has been marketed by Boeing as a competitor to the 5th gen F-35. But it's lost every competition where it's gone head-to-head against the F-35. The F-15SE has been tweaked to be stealthy against air-to-air radars, but it's not quite as invisible to larger ground-based radars. If you look at the F-15SE from any direction other than head-on, it's a great deal less stealthy than the F-35.

Cost doesn't seem to be much of a factor here. The two jets are within shouting distance of each other. The Israelis are picking up their brand-new F-35s at about $110 million each; the F-15SE comes in just a bit below that, at about $100 million per jet. And really, what's another $10 million or so between friends?

It's important to note at this point that, to many people, it's an absolute article of faith that the F-35 is a terrible, horrible, no good, very bad plane. If that's the case, they might expect the Israelis to skip the F-35 altogether in favor of getting more F-15SEs.

Advocates of the F-35, who claim it is the best thing since powered flight, similarly have a hard time explaining why the Israelis — who are already committed to buying a bunch of F-35s — would turn around and buy the F-15SE, the plane that keeps losing in competitions to the F-35.

Now, sure, the Israelis could reverse-engineer the F-15SE and also do homebrew modifications to their existing fleet of F-15 aircraft to upgrade them all to 4.5 gen. But that still leaves them with a large number of F-16s, and if they wanted to upgrade those as well, then they should have asked for a squadron of the newest 4.5 gen F-16s. They haven't. In fact, the long-term plan is for Israel to replace all of its F-16s with newer F-35s. Replacing the F-16s with F-35s and upgrading F-15s to F-15SE. Well, maybe, maybe not. The Israeli Defense Ministry isn't sharing all of its top-secret plans with me right now, so let's move on.

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The long and short of it is that, overall, it doesn't make a lot of sense for Israel to buy both the planes that won and lost in head-to-head competition, and there are a few theories about what's going on. This one probably won't explain all of it, but may shed some light on some of the decision-making.

There's a dirty little secret that's just barely starting to bubble up. It'll be a few years before it's widespread conventional wisdom, but if you listen very, very closely, you can hear it being whispered: Stealth ain't gonna be around forever, folks.

In a speech last February, then-Chief of Naval Operations Admiral Jonathan Greenert was quoted by the US Naval Institute News as saying: "I don't want to necessarily say that [stealth is] over but let's face it, if something moves fast through the air and disrupts molecules in the air and puts out heat — I don't care how cool the engine can be — it's going to be detectable."

And it's not just the heat generated by air friction that could be stealth's undoing. This Aviation Week article notes: "Low radar cross section is a niche capability, and new sensor technology advances can make it less important. China, India and Russia are already finding weaknesses in stealth as they develop it for their own advanced strike aircraft." The story then goes on to quote a senior Israeli Air Force official as saying (of the F-35) "We think the stealth protection will be good for 5–10 years, but the aircraft will be in service for 30–40 years."

In terms of technology programs, five to 10 years is more or less an appropriate length of time to develop a new, medium-to-high complexity system based on well-understood physics. So, if the Israeli guy isn't just pulling a number out of thin air, it would suggest that somewhere folks have just about cracked the stealth code and are now beginning work on operationalizing it somehow. Granted, it may not have anything to do with that air-friction trick Greenert mentioned, but a lot of very smart people all over the world have been working on defeating stealth, so it's only a matter of time before someone figures out how to beat it.

And this gets back to something inherent in 5th gen designs. Remember how 5th gen aircraft need to be designed from the ground up as stealth aircraft to maximize their ninja-like ability to avoid radar? Well, that design choice comes at a price. A 4th gen aircraft might be designed to balance speed, range, and payload. But if you add an additional requirement, like stealth, it makes the design more complicated. It won't perform as well in terms of speed, range, and payload. It doesn't matter what the specific capability you're adding happens to be: it could be air-to-air capability, ability to pound ground targets, sensors, what have you. The bottom line is the same, adding performance objectives leads you ever closer to being a jack of all trades and master of none. And in this case, 4.5 gen aircraft have a key advantage: they were never built with stealth in mind.

In other words, once you throw all the stealth stuff out the window, a 4.5 gen aircraft may be able to outperform a 5th gen aircraft. Thus, if stealth didn't matter at all, maybe the F-15SE could beat the F-35 head-to-head. But even something that degrades stealth capability somewhat won't mean that the stealthiness is completely going to disappear. So, right now, buying both the F-35 and F-15SE means that whether stealth is degraded only a tiny bit or a lot, they're covered.

The Israeli Air Force may find itself operating over countries with vastly different technological capabilities. At one end, you have places like Iran sporting some serious high-end Russian air defenses. At the other end of the spectrum, some countries in Israel's neighborhood, like Yemen, do not even have a proper air force.

By adding the 4.5 gen Silent Eagle into the mix, Israel will have a whole host of planning options. In a super intense environment, they could pair F-35s with F-15SEs and leave everyone else at home. If the threat was intermediate, they could treat both the F-35 and F-15SE as the high-end aircraft and pair them with the older 4th gen stuff. Even without doing all the number-crunching, it seems that this purchase will just about double the number of Israel's deployment options.

If adding the not-quite-top-of-the line 4.5 gen stuff to the mix really does double the fun, then countries like Russia and China that are developing both 4.5 gen and 5th gen aircraft may find that they can do a whole lot more with the mix than they can by limiting themselves to either one or the other.

This, in turn, has further implications for US decision-makers on what they need to plan for down the road. But that's a whole different discussion about aircraft buys and industrial base and all that stuff. If I were an industry watcher, I'd be paying very close attention to how countries are thinking about balancing 5th gen, 4.5 gen, and 4th gen aircraft over the next five or so years as a very early leading indicator of how we should all place our bets about when we'll see the end of the decades-long dominance of stealth technology.

Follow Ryan Faith on Twitter:__@Operation_Ryan