A Russian Tupolev Tu-154M spy plane Alan Wilson Last week, a Russian military reconnaissance aircraft conducted an aerial inspection of US military sites in California and Nevada and intercontinental ballistic missile silos across the Midwest.

This spy plane — which looks looks like an ordinary civilian airliner to the uninitiated but is really loaded with advanced reconnaissance equipment — flew over sensitive defense installations, carrying out detailed observations over several flights.

It was carrying several military officers from foreign nations as it gathered intelligence on American bases. And its flights originated from Travis Air Force Base in California with the full knowledge and assistance of a small group of US Air Force personnel and senior US government officials.

Sounds like some weapons-grade tinfoil-hat conspiracy gibberish, doesn't it? Except it's totally true.

The idea that Russian military aircraft are flying over American bases with American permission sounds like a nutty overreaction to increased worldwide patrols of Russian nuclear bombers and other combat aircraft, sneaky submarine business in national waters, and other retro-Cold War shenanigans. However, it's actually just run-of-the-mill stuff that the US and Russia (along with 32 other nations) are doing regularly under the Treaty on Open Skies.

Open Skies permits signatory nations to carry out reconnaissance overflights of other signatory nations without interference, though some terms and conditions apply. Basically, a bunch of countries agreed to the familiar arrangement, "if you show me yours, I'll show you mine" — only this is less "playing Doctor" and more "playing Doctor Kissinger."

President Dwight Eisenhower first pitched the idea of sanctioned peeping in 1955 at the Geneva Conference as a proposal for "mutual aerial observation." This was soon followed by another historic first at the Geneva Conference, when Soviet Premier Nikolai Bulganin promptly rejected the idea.

The US read on the Soviet rejection might be that it meant the Soviets were up to no good and wanted to keep all their mischief under wraps. However, it could just be that the Soviets suspected Americans of trying to pull a fast one and do something sneaky and dishonest under the guise of such an arrangement. A US Hawkeye spy plane US Navy/Getty Images

Either way, there wasn't sufficient mutual trust for an agreement, which isn't a surprise when both sides have tons of nuclear and conventional weapons pointed at each other.

A mere four decades and change later, the idea was resuscitated in 1989 by President George H. W. Bush, which lead to the 1992 signing of the Treaty on Open Skies by the then-members of NATO and the Warsaw Pact. The treaty's provisions entered into effect in 2002, and since then recon aircraft full of gear and international observers (to make sure the overflights comply with treaty terms) have been flying over all sorts of military installations with nary a hiccup (well, almost).

Now any of the 32 signatories can (and often do) carry out overflights according to the provisions of Open Skies. Like last week's Russian flights, US aircraft regularly overfly Russian military installations with Russian permission using a variant of the venerable Boeing 707 airframe, kitted out for reconnaissance.

While an international agreement allowing spy plane overflights still might smack of One World Government conspiracy theories, there's actually quite a sane point to the Treaty on Open Skies. What's tricky is that it's one of those things that makes sense on a surface level but doesn't really make sense when you think about it, but then if you dig a bit deeper still, it makes sense again.

At a surface level, Open Skies is what diplomacy wonks refer as a "trust and confidence building measure," which is exactly what it sounds like. It's like those trust falls and team-building exercises that folks occasionally get sucked into, except it's for countries and not nearly as liable to result in hilarious workers' compensation claims.

But if you think about it a bit more, that premise starts to appear to unravel. You might wonder, for example, what do recon flights under the treaty accomplish that's different from the work of satellites and unapproved spy planes?

Consider that planes are closer to the ground than satellites, and should therefore be able to get better pictures. But the treaty limits the kinds of sensors that can be used on the planes, meaning they actually produce lower quality pictures than you can buy from commercial satellite imagery companies, let alone what modern spy satellites can see. A US U-2 spy plane Master Sgt. Scott T. Sturkol

Another point you might weigh is that, since satellites have predictable orbits, it's easy for a country to figure out when everything needs to be covered up to hide it from satellite observation. But Open Skies flights have to give at least 24 hours notice, so there's still an opportunity for everything to get hidden ahead of even the most "surprising" inspections.

You can go back and forth about the pros and cons of Open Skies-based monitoring versus other platforms, quibbling until you're blue in the face, but there are two main points worth noting. The first is that not all signatory nations have specialized reconnaissance aircraft or satellites. The treaty makes allowances for this, permitting a nation to use an approved aircraft from another signatory.

The second point is that the main purpose of Open Skies isn't really about collecting information. When strategic planners thing about the future and try to plan around future hypothetical dangers, they can basically look at intentions or they can look at capabilities.

Working with intentions is pretty much the only way to go when you're figuring out allies. The US doesn't plan on waging war with Canada or the UK (and hasn't for nearly a century.) That's basically an intent call; since the end of World War II, there really haven't been any meaningful scenarios that would threaten to prompt full-fledged fighting between the military powers of the English-speaking world.

So the US just assumes that there are some countries it will never end up fighting. Developing contingency plans for a war against both enemies and allies is a surefire way to end up drafting everyone and preemptively invading the world.

So planners generally assume they'll only be fighting bad guys. But when it comes to planning for war with potential adversaries, there aren't a lot of good ways to figure out what a prospective enemy might or might not get up to if they have the appropriate capability. In a full-scale war with China, how confident could the US be that China might not attack American forces based in Japan or Korea? Hard to tell, right? Those are unknowable questions of future intention. Russian Tupolev Tu-154M spy plane Alexander Mishin

Planning for conflicts with potential opponents means assessments are made based on capabilities. And when that's the mindset, planners always figure on the worst-case scenario. If you think your opponent might have between 700 and 900 tanks, then planning to deal with 900 or 1,000 tanks (just to be sure) means you'll be able to handle 700 tanks no problem. But if you guess lower than the actual number of tanks, you're hosed.

Therefore, when military planners are figuring things out, there are basically two extremes toward which planning gravitates: planners either assume that there will be no chance of conflict, or they assume the worst.

This tendency to always plan based on the worst-case scenario is part of the purpose of Open Skies overflights. By basically extending an open invitation to any other country to come fly over and take a peek at what's going on, it helps put an upper limit on the planner's worst-case scenarios. While the imagery provided by an Open Skies overflight might have its limitations and not be super-high resolution, it provides a transparent method of keeping an eye on what's happening over on the other side.

In a sense Open Skies flights are an analog to inspections carried out under non-proliferation treaties or agreements concerning weapons of mass destruction. Consider the case of Iran.

There has been much back and forth between Iran and its counterparts in the ongoing negotiations over the country's nuclear program. Iran wants to limit what foreign and international weapons inspectors can inspect, either because they don't trust the West not to get up to some funny business in those inspections or because they have something to hide. This is the same thinking that attended the Soviet rejection of Eisenhower's proposal in 1955.

Meanwhile, the West is claiming that they cannot be expected to take Iran's word on its nuclear program unless an inspection regime can verify Iranian claims. And until the West trusts Iran, the West won't agree to lift sanctions on Iran.

So when all is said and done, Open Skies is basically a post-Cold War verification and inspection regime between NATO and the former Warsaw Pact countries — or, in other words, between the US and Russia and their respective allies. But it's not really tied to one specific arms control or verification issue. It's a much broader proposition: countries participate because it can add some transparency and verification where trust in another party's intent alone is insufficient to eliminate doubt.