I find it amusing that something like this would even be a topic. A small nation in the ass crack of the world is going to be able to stand up against the most dominate force the Earth has ever seen?
For those who think it will be bad for the US then I think you need to go check out their military capabilities for overseas. It doesn't take much thought to figure out that Iran has no chance of even striking the US mainland militarily whereas the US has the capability to attack any part of their country without even being in it.
America would crush Iran, but Iran could do a lot of damage back. The US military is built for superior capabilities but Iran practises asymmetric warfare. Your navy brings a destroyer? Good luck when it gets swarmed by a hundred speedboats packed with explosives. Do not underestimate your enemy, but then.. I guess no Americans here would actually be putting their lives on the line in the military.
Assuming everyone on the destroyer would be asleep and not doing their job sure, 100 speedboats with bombs on them might work. Then again, these ships have high tech radar and weapons systems that could rip them to shreds using only their cannons and machine guns. This is just from one ship, US Navy ships travel in battle groups which often include aircraft carriers.
It would be a pipe dream for anyone to blow up a US Destroyer using speedboats.
USA would erase Iran from the map in a very short time but It won't be for free. Russia and China won't watch it like a video game. They would hit USA back. Believe me they would do it. Why? Because they know if they give up on their friend, they are the next.
It is like Lions and Zebras. Stupid fuck zebras always give away someone from their group to the lions so they can leave the threat without any effort.
If they were able to organize an attack to the lion group, they would have saved that poor zebra.
Elephants so that sometimes btw.
If you can't beat someone who is a lot stronger than you, you need to make allies.
What does Iran provide Russia and China that would encourage them to face all out war with the US?
I already said it. If they don't face the danger as a group in the right time just when Iran is being attacked by the USA, they will lose 1 ally for free.
And what happens when the USA decides to fuck China up after Iran? Russia can say its not my business, I don't care.
But... lets take a guess who would be the next after China?
Humans have one trait that has allowed us to survive for this long, self preservation. Countries are much more willing to sit back and let others get destroyed if they can get by unharmed regardless of the consequences. This is why Russia, China, and Iran have sat back and done nothing while we, the US, have invaded country after country after country for decades.