I think that the take~down happened in international waters. The Iranians would have known to the minute when the boats were leaving Kuwait, and their probable course to Bahrain, so an intercept would be simple. They know our ROE would be "Do not shoot EVER unless you are fired upon first. PERIOD!!!"
So, if the Iranians jam our boats so they cannot communicate, and then swoop in close, it's almost a guaranteed outcome. They KNOW we won't shoot first! So by coming in closer and closer with weapons aimed at our sailors, overwhelming them with numbers at point-blank, then on loudspeaker they say, "Step away from your weapons or we will slaughter you!" At that point, it's a fait accompli. Once our sailors step back from their guns, it's over. Next, "Take off your jackets and weapons " etc, until they are in t~shirts only. Then “Kneel down!"
Step by step they get their way, based on a deep understanding of our ROE and our responses at every stage. Once they have control of our boats, they can drive them to Farsi Island, and remove every single GPS device, radar, cell phone etc. Then, there can be no proof of where the attack happened. And worst of all, Obama and Kerry are happy to go along with the lie, in order not to upset the nuclear deal applecart.