Any big-ticket military technology purchased from the US comes with rules. Big stacks of strict guidelines outline exactly what allies can do to the hardware and the systems that run it. Generally, it comes down to: nothing. No modifications, no additions, no deletions. You can't even make repairs without written consent from the Pentagon.

Uncle Sam typically responds to such requests with a resounding no, especially when the hardware in question is the wildly advanced (and wildly over budget) F-35 Lightning II Joint Striker Fighter. The stealth fighter jet, which Lockheed Martin is selling to US allies, comes with caveats that expressly prohibit unauthorized tinkering and a requirement that only US-run facilities service the plane. These rules, designed to protect deeply intertwined systems and maintain the security of sensitive technology, are non-negotiable.

Unless you are Israel.

Israel will be the first ally to receive the aircraft when its deliveries begin in December, and it will for the foreseeable future be the only country allowed to install customized software and weapons. The software is an app-like "command and control" system used elsewhere in the Israeli Air Force's fleet; the weapons would initially be an Israeli-built missile system. The US will most likely also let the Israeli Air Force service the jets independently.

The negotiations are still ongoing within Lockheed Martin and the Pentagon's F-35 Joint Program Office, which grants such approvals. Final decisions are expected this year. One reason Israel gets a pass is because of its technological track record, particularly with US weaponry. Israel's Air Force has long tweaked F-16s and F-15 to integrate its own systems.

Israel is quite adept at building advanced military technologies, from weapons systems to sensors to communications gear, and sells a lot of it to the US. Israel's Litening precision targeting system—an external pod that uses infrared imaging and laser range-finding to guide bombs to targets—is used in a variety of US Air Force and Navy aircraft. The sophisticated Joint Helmet-Mounted Display system for F-22 fighter pilots leans heavily on Israeli technology.

But an even bigger part of the explanation has to do with Israel's state of perpetual conflict, which makes it a different sort of ally for the US. Speaking at a conference last month in Tel Aviv, as Defense News reported, Israeli Air Force chief of staff Brigadier General Tal Kalman suggested Israel’s “unique requirements” justify a degree of autonomy with the F-35. Israel is pursuing its own maintenance center at Nevatim Air Base, where the jets will be based. When you might go to war at any moment, the argument goes, you can’t have your best hardware go out of service for weeks at a time for checkouts that can take just a few days on your own turf.

Israel receives about 55 percent of the State Department's Foreign Military Financing budget, according to Defense News. A new agreement currently being negotiated could see $40 billion go to support Israel's military needs over the next 10 years—a number that Israel currently thinks is inadequate, given how much technological advancement its regional adversaries, primarily Iran, have recently clocked.

From that perspective, what helps Israel helps the United States–and the F-35 will give Israel an overall airpower advantage that could last decades. But system security remains a key concern for the US. It helps that the key piece of software Israel is adding to the F-35I (its official designation) won’t affect the airplane’s own software. It’s a free-standing, add-on app for what’s known as C4 systems—command, control, communications and computing. The app draws data streams from the F-35's own open-architecture operating system in order to provide additional functionality. According to Benni Cohen, a general manager at Israel Aerospace Industries, the state-owned military technology developer that’s creating the new app, it gives the air force an easy tool for adapting the F-35 to its own needs. “[Our] open-system architecture enables rapid software and hardware development cycles that will also provide more affordable modernization and support of systems over the platform’s life cycle,” Cohen said.

It will also allow easy integration with the current systems used by the Israeli Air Force, including those within the force’s existing F-16 and F-15 fighters, Cohen added. Variations of the same software slated for the F-35 already exist in those fighters imported from the United States. The F-35 will effectively "play nice" with the IAF's current resources.

The other nations buying the F-35—the UK, Italy, the Netherlands, Turkey, Australia, Norway, and Denmark—have spent years negotiating how much they'll be allowed to tinker with the jet. None have had the success that Israel appears to be achieving. Beyond the app integration—which may actually inspire other program partners and customers to pursue similar tactics, according to Aviation Week & Space Technology—Israel will likely also add its Spice 1000 precision missile system, among other possible weapons, along with so-called conformal fuel tanks, which mount above the wings and close to the fuselage, to the fighter. Though they could extend the fighter’s range by up to 40 percent, those tanks will likely compromise the jet’s stealth capability.

The US is working with Israel to ensure that all their proposed systems will work harmoniously with the F-35’s native systems, and that its proposed maintenance facility at Nevatim air base will be adequately secure. When the jets start arriving later this year, Israel intends to make then fully combat-ready within just 12 months.