The war between the U.S. and Iran has now become nothing more than a classic war of attrition. The key question is: which side will run out of missiles first? Nobody knows the answer to that, but every day that Iran and the U.S. trade attacks with each other brings the answer closer and makes it more critical. In the future, this war will doubtlessly be studied as a new paradigm for modern warfare that is similar but different in one big way to the war being waged between Ukraine and Russia -- since neither Iran nor the U.S. is able to easily and quickly replace their dwindling stockpiles of crucial munitions. Which makes it a textbook example of a war of attrition.

Both Russia and Ukraine have shown astonishing resilience in being able to continuously produce drones and missiles to launch at each other. Iran, however, cannot easily replace its arsenal of missiles, because the U.S. has bombed so many factories and production centers that that ability no longer exists for them. They may still be able to produce some cheap (and rather low-tech) drones, but not ballistic or cruise missiles. Iran has a finite stock of those, at least for the time being (until they can rebuild their production lines, which will likely take years). How many missiles does Iran still have left? We don't know. There are estimates, but the only ones who really know are the Iranians.

The U.S. has its own stockpiles of weapons, both offensive and defensive. The offensive weapons (cruise and ballistic missiles) aren't that important to the war effort any more, since America has full control over Iran's skies at the moment. There is no need to launch missiles from hundreds of miles away when you can fly a plane over and drop as many cheap, easy-to-produce bombs as you wish, to put it bluntly. So nobody is all that concerned over how big our stockpiles of Tomahawk missiles are, at this point. The offensive phase of the war when they were necessary is over.

What is concerning the war-planners much more is America's dwindling stockpile of anti-missile interceptors. Patriot missiles (and their close cousins with slightly different capabilities) are being used to defend U.S. bases and other infrastructure within our Gulf allies from Iranian missile and drone attacks. And these supplies are almost as finite as the Iranian missile supply -- not because Iran somehow bombed our factories or production facilities, but because these high-tech interceptors are so complicated (and expensive) to build. With the production lines we currently have, it is going to take years to replace what we've already used up in the Iran war in just a few months. And due to this extended timeline, our stockpiles simply cannot be replenished faster than we are using the missiles up. So while we do still have some new missiles being built and delivered, their numbers aren't great enough to solve the attrition problem.

Unlike estimates of the enemy's supplies, American leaders do know how many missiles we have left and the exact timelines necessary for their replacement. But the public doesn't know, since these are a closely-guarded military secrets (for obvious reasons). All we can do is observe the changing ways our leaders are waging this war.

A while back, I read a comment from a Ukrainian soldier who had travelled to the Gulf region to observe how the U.S. was fighting its war, and to offer his advice using his experience fighting a war of drones. He expressed his astonishment than the U.S. was using two interceptors to shoot down single incoming Iranian missiles. This was apparently standard doctrine for the U.S. forces, since interceptors are not perfect. If one interceptor missed, then the second one would hopefully succeed and knock down the incoming missile or drone. But this churns through the interceptor stockpiles twice as fast, obviously, which was why the Ukrainian was so astonished.

One has to wonder if that military doctrine (of shooting two interceptors off as standard procedure) is still being used today. Because in the recent two-week exchange of fire with Iran, the media reported that some Iranian missiles were being allowed through the interceptor defenses -- incoming ballistic missiles whose trajectory showed that they wouldn't hit any troops or critical infrastructure were being essentially ignored. This shows that the interceptors' use is already being triaged and held back for only the most threatening of the incoming fire.

One strange development that nobody has an honest explanation for (Trump's words on the subject are, as usual, completely unbelievable) is the "pause" that we are currently experiencing. After bombing Iran for almost two solid weeks every single night, the U.S. suddenly just stopped. There were no diplomatic developments or ceasefire negotiations taking place at all. We just decided to stop attacking, and Iran followed suit.

Could it be that both sides are simply running out of missiles? That is pure speculation, but it certainly is plausible, at this point. How many missiles and drones does Iran still have available to it? How low are the stockpiles of U.S. interceptor missiles getting?

America's missile stockpiles haven't completely disappeared, it bears mentioning. But America is in a much different military position than Iran. We have to not only concern ourselves with the war we're fighting right now, but we have to also be prepared for other conflicts in other regions of the world as well. We have to worry about China and Russia, and hold back enough missiles to still be a credible threat to both of them, to deter a move such as China invading Taiwan. So we can't use up all our interceptors defending against Iranian attacks. Iran doesn't have that problem -- they are at war with us, and that's their only military concern at this point. They have to hold back enough drones and missiles to continue to threaten shipping, but that's their only restraint.

In a classic war of attrition, whichever side has more supplies eventually wins. If we were to run out of interceptors (the ones available in the region), then Iran could attack U.S. bases at will. The U.S. military already was forced to abandon one major base in the Gulf region, and pull the unit back to Florida. Other bases could be abandoned as well, if the stockpiles of interceptors run low enough. Military retreats are not exactly victories, to state the obvious.

The other scenario would happen if Iran runs out of missiles and drones, which would mean they would not only be powerless to attack us, but also that they would likely lose the control over the Strait of Hormuz that they have won in the midst of this war. If they had no way to attack ships passing through the waterway, then their threats would be a lot emptier (they do still have mines, however, it should be noted).

All of this adds up to a gigantic game of "chicken," where both sides must show strength during the periods when we are exchanging fire with each other. Neither side can afford to give the impression that they are concerned with how fast the munitions are being used up. Iran already won a big victory in this regard, early in the war. Trump boasted that America had absolutely obliterated Iran's military, but they somehow were still able to keep launching missiles and drones. An intelligence report from our side then showed that Iran had actually retained about 70 percent of its missile capabilities, even after all the initial U.S. attacks. That was months ago, though. They've fired off many more missiles since then, and some of the U.S. bombing attacks must have been at least partially successful in wiping out some of Iran's missiles.

But it really comes down to which side is more afraid of running out of missiles first, at this point. Is the Pentagon telling Trump in no uncertain terms that they simply cannot sustain active warfare against Iran without any end in sight? Was that the reason why the recent pause in fighting happened? Even if that is not the sole reason, it has to be a big concern on our side. At some point we're going to have used up so many interceptors that to continue to defend our forces in the region would mean pulling stockpiles meant for elsewhere (Asia or Europe). This would create a dangerous lack of capability that other countries may successfully exploit in the future.

China, in particular, is a powerhouse when it comes to manufacturing capabilities. And the lesson they may be learning from all of this is that the way to defeat the vaunted U.S. military is to stockpile so many offensive missiles and drones that they simply overwhelm our defensive capabilities. After all, if a nation as small as Iran can manage to back us into the corner in a war of attrition, then it wouldn't be that hard for a much larger nation with a much more robust manufacturing base to not only force us into a stalemate, but to actually defeat us. All they'd have to do is produce drones and offensive missiles by the thousands -- or by the ten thousands. Having that many on hand would almost guarantee that they'd win, in the end. That's the grim reality that this current war of attrition has exposed.

-- Chris Weigant

Follow Chris on Twitter: @ChrisWeigant