WASHINGTON — Iran has expanded its naval presence in the Straits of Hormuz, the passage for an estimated 40 percent of global crude oil shipments.  
The U.S. Navy has determined that Iran has amassed a fleet of fast patrol boats in the 43-kilometer straits. Iran's Islamic Revolutionary Guard Corps, responsible for strategic programs, leads the effort.
At this point, officials said, IRGC has deployed more than 1,000 FPBs in and around the straits. The vessels, armed with cruise missiles, mines, torpedoes and rocket-propelled grenades, are up to 23 meters in long and can reach a speed of 100 kilometers per hour.
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"This marks the implementation of Iran's swarm program, where dozens of armed speed boats attack much larger naval vessels from all sides," an official said.
In 2005, IRGC developed its swarm doctrine following Teheran's assessment that the United States was considering an air strike on Iran's nuclear facilities. Officials said the swarm doctrine was designed to exploit the slow pace of U.S. aircraft carriers and destroyers in the shallow waters of the Gulf.
"Iran still states that the Iranian Revolutionary Guard Corps will employ swarming tactics in a conflict,'' U.S. Office of Naval Intelligence spokesman Robert Althage said.
IRGC swarming tactics envision a group of more than 100 speedboats attacking a target, such as a Western naval vessel or a commercial oil tanker. They said 20 or more speedboats would strike from each direction, making defense extremely difficult.
The Navy, with at least two carrier groups in the Gulf, has been developing counter-measures to an Iranian swarm attack. These include using minesweepers, unmanned aerial vehicles to monitor Iranian speedboats and the deployment of weapons that could blast Iranian speedboats at standoff range. Such exercises have been conducted over the past few months.
"We have devised various tactics and other ways of coping," U.S. commander Vice Adm. Kevin Cosgriff said. "You just don't get 1,000 or 500 or even 20 of anything under way and tightly orchestrated over a large body of water to create a specific effect at a specific time and specific place. They have their own challenges.''  
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