Center for a New American Security

Five Iranian speedboats harassed three US navy ships at the weekend, approaching them and radioing a threat to blow them up, US officials say.

The incident happened as the US vessels passed through the Strait of Hormuz, which separates the Arabian peninsula and Iran, Pentagon officials said.

US sailors came close to opening fire, unnamed officials told CNN.

The White House on Monday warned Iran against "provocative actions that could lead to a dangerous incident".

Abu Muqawama walked into a coffee shop this morning and saw Barbara Starr on the television explaining this weekend's nonsense about Iranian naval vessels threatening U.S. warships in the Strait of Hormuz.* There is going to be a lot said about what this "means" and the way in which Iran is flexing its muscles in what it considers to be an "Iranian Lake" (rather than an international waterway). But we don't do strategy here at Abu Muqawama, preferring as we do to focus on tactics. So this would be a good time, then, to provide a link to this piece by Fariborz Haghshenass on Iranian naval tactics. Haghshenass is the nom de plume of a former Iranian military officer who often writes on Iranian military capabilities.** This "explainer" piece is a good one:

Iranian naval swarming tactics focus on surprising and isolating the enemy’s forces and preventing their reinforcement or resupply, thereby shattering the enemy’s morale and will to fight. Iran has practiced both mass and dispersed swarming tactics. The former employs mass formations of hundreds of lightly armed and agile small boats that set off from different bases, then converge from different directions to attack a target or group of targets. The latter uses a small number of highly agile missile or torpedo attack craft that set off on their own, from geographically dispersed and concealed locations, and then converge to attack a single target or set of targets (such as a tanker convoy). The dispersed swarming tactic is much more difficult to detect and repel because the attacker never operates in mass formations.

...

In wartime, Iranian naval forces would seek to close the Strait of Hormuz and destroy enemy forces bottled up in the Persian Gulf; therefore speed and surprise would be key. Iranian naval forces would seek to identify and attack the enemy’s centers of gravity as quickly as possible and inflict maximum losses before contact with subordinate units were lost as a result of enemy counterattacks. Geography is Iran’s ally. Because of the proximity of major shipping routes to the country’s largely mountainous 2,000-kilometer coastline, Iranian naval elements can sortie from their bases and attack enemy ships with little advance warning. Meanwhile, shore-based antiship missiles can engage targets almost anywhere in the Persian Gulf and the Gulf of Oman. To achieve the latter capability, and to improve the survivability of its shore-based missile force, Iran has devoted significant efforts to extending the range of locally produced variants of a number of Chinese shore-based antiship missiles such as the HY-2 Silkworm and the C-802 (from 50 to 300 kilometers and from 120 to 170 kilometers, respectively). It has also introduced the use of helicopter-borne long-range antiship missiles.

To ensure that it can achieve surprise in the event of a crisis or war, Iran’s naval forces keep U.S. warships in the region under close visual, acoustic, and radar observation. The Iranian navy commander—Rear Adm. Sajad Kouchaki, one of the architects of the country’s naval doctrine—recently claimed that Iranian submarines continually monitor U.S. naval movements, frequently at close range, and have even passed underneath American aircraft carriers and other warships undetected. Iranian UAVs also frequently shadow U.S. carrier battle groups in the area.

*Abu Muqawama is a big fan of CNN's Pentagon reporter, Barbara Starr. She was a really good print reporter for Jane's before she made the switch to television. In other words, she wasn't put in front of the camera just because she was blonde and bubbly. She is neither. (Allegedly, another U.S. news network does this. Not gonna say which one.) Barbara Starr's producer is also really smart and has covered defense issues for a long time.
**For those who want more on this, UK-based analyst Martin Murphy also works a lot on Iranian swarming tactics.

UPDATE: This was cross-posted over at Danger Room and generated, like, 100 comments or something. Jeez...