September 25, 2012 -- As Iran and the United States trade diplomatic jabs before a global audience at the United Nations in New York, their two militaries are simultaneously conducting shows of force just off Iranian shores -- and just a few hundred miles away from each other.
The U.S. has flooded the Persian Gulf with the largest armada ever gathered for a military exercise. More than 20 ships and participants from every continent except Antarctica are practicing a mission to keep Gulf waterways free from mines.
U.S. officials emphasize it is a defensive training mission, but analysts say it is clearly a warning to Iran, which has threatened to close the strategic Strait of Hormuz in case of an Israeli assault. The U.S. will keep its warships in the Gulf even after the exercise is over.
"Any extremist group, any country that puts mines in the water would be cautioned" by the exercises, Gen. James Mattis, the U.S. Central Command chief, told reporters onboard the U.S.S. Ponce last week. "We do have the means to take mines out of the water if they go in. We will open the waterways to freedom of navigation."
Iran, in turn, announced today it had launched four surface-to-sea missiles near the Strait and destroyed a target the size of a warship. Gen. Ali Fadavi of Iran's Revolutionary Guard told the semi-official Fars news agency that Iran planned a "massive naval maneuver in the near future," repeating a threat from other Iranian officials in the last month.
The gunboat diplomacy occurs as tensions between Iran, the United States and Israel publicly intensify, and leaders in all three countries openly discuss possible military action. Israel has been increasingly aggressive in public statements in the last few weeks and warns that Iran could be within six months of obtaining a nuclear weapon.
"They're in the last 20 yards, and you can't let them cross that goal line," Israeli Prime Minister Benjamin Netanyahu told CBS News' Meet the Press last Sunday. "You can't let them score a touchdown, because that would have unbelievable consequences, grievous consequences for the peace and security of us all, of the world really."
Iran denies it is pursuing weapons and insists its nuclear program is for civilian power purposes.
Sunday a senior Iranian military official threatened U.S. bases in the Persian Gulf in the case of an Israeli attack, and Monday in New York, Iranian President Mahmoud Ahmadinejad belittled Israel, saying the Jewish state was historically insignificant compared to Iran.
"They have no roots there in history," Mr. Ahmadinejad said of the Israelis. "They do not even enter the equation for Iran."
In the event of military action, Iran has threatened to try to close the Strait of Hormuz by laying as many as 5,000 mines, according to U.S. estimates. The strait, just 21 miles across at its narrowest, is a vital waterway for oil transportation through which an estimated one fifth of the world's oil travels.
"If there are mines in the waters, it's good to bring the global talent together and practice before you might need it one day. And that's what this exercise is all about," Captain Jon Rodgers of the U.S.S. Ponce, which is taking part in the exercise, told ABC News in an interview aboard the ship last week. "The threat is there. My job is to make sure that this crew is ready for anything."
The buildup is unmistakable. Two aircraft carriers are in the region, where there was only one between 2003 and 2007. The U.S. is building a missile defense radar station to defend against Iranian missiles that can currently reach eastern Europe, as first reported by the Wall Street Journal. And the U.S. has doubled the number of minesweeping boats currently deployed to the Gulf -- to four to eight -- or more than half of the American minesweeping fleet.
ABC News visited one of the newly-arrived minesweepers, the U.S.S. Warrior, during a trip organized by the Navy last week. Captain Scott Nietzel, 34, showed off the tools he uses to hunt for mines, including a drone submarine that beams back both pictures and sonar signals to help the crew determine the location of possible mines, a device that can fakes a ship's magnetic signature and tricks mines into exploding in wakes rather than underneath ships, and underwater bomb squads.
"The idea of a minehunt is you go out, you find them individually, and you neutralize individually. So it's very much like finding weeds in the grass. Find what doesn't belong," Nietzel said. "We're not just digging through the haystack looking for the needle. We have a way to chop the haystack up into chunks, to go through them methodically, and guarantee what we've gotten out of there is the needle and leave the hay for another day."
But despite the diplomatic and naval tensions, U.S. sailors say they regularly encounter Iranian ships in the Persian Gulf and that the meetings are without tension.
"We talk to each other on the radio. Sometimes we encounter each other. We're both navies operating on international waters. We extend professional courtesies to each other," Nietzel said. "Certainly we're cautious and take care of ourselves. [But] everything we've seen so far is very professional and very routine."
Still, the sailors are on high alert, and the tensions simmer just below the surface. In July, the U.S.N.S. Rappahannock fired on a small Indian fishing vessel just west of the Strait of Hormuz after it ignored orders to turn away, killing one and injuring three.