The Iranian Navy is the one branch of their armed forces that is always in contact with U.S. forces, and would be the first to engage if things got out of hand. The backbone of this navy is a force of missile-armed patrol craft, the modern equivalent of the PT boats that were so famous during World War II. Missile-armed patrol boats made their mark when two Komar-class boats sank an Israeli destroyer in 1967.
If only we had some way to get troops into Iran without needing to make an amphibious landing. Bases and overflight rights for neighboring nations sure would come in handy, but the utter lack of a plan and general cluelessness have left us without an opportunity to attack or even threaten to attack with heavy forces and with no real options regarding Iran.
If only we had thought of this sooner.