You made it a point to specifically tie Iran and Iraq together as one in the same yet Iran of 2019 has so much more operational abilities than Iraq of 91′ did since Iran’s method of engagement will be asymmetrical. Iran has drones constantly giving live information on U.S. movements in and around their borders and coast, Iran has ELINT capabilities to assess what the U.S. is planning on doing, Iran has the kinetic option to destroy U.S. naval assets and U.S. air force bases in Saudi Arabia, Qatar, Kuwait, Bahrain etc….Iran can and will call upon its allied militias in Iraq, Syria and Lebanon to start attacking U.S. interests in the region (bringing in Hezbollah into the equation is a whole other ball-game).– Iraq did not have any of this but Iran does. Iran is a different beast to tackle due to its nature of networking and fortifying stratergic assets in-case of a shooting war.
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The bases have a natural defense, that being the mountains and as aforementioned, these underground bases have earth moving equipment to bore new holes if need be. The efficacy of stand-off U.S. military munitions will be tested greatly, these mountains are sharp and jagged. I would surmise that the US military will have to fire large salvos of tomahawks and other stand-off munitions due to attrition of the missiles hitting the terrain or not getting the desired effect they want. This is all happening whilst Iran is raining 100s of missiles on U.S. bases all over the Middle-East. This is something that Iran can keep up for a good amount of time, so don’t think it’s a one and done kind of thing. Some other things to mention are the various weapon platform Iran can employ its missile arsenal on; TELs, Trucks, Stationary batteries, mobile trucks that house missiles inside the Cabin, submarines: many of these are mobile and are hard to retaliate against no matter how good your reconnaissance and Air-force capability are.
To sum it up, Iran’s mountains will defend Iranians strategic assets during the onset of the war, forcing the U.S. to have to put boots on the ground