The U.S. Navy released video and images showing an encounter between two U.S. Coast Guard cutters and an Iranian Islamic Revolutionary Guard Corps Navy (IRGCN) catamaran in the Persian Gulf earlier this month. At the time, the U.S.  vessels were conducting routine maritime security patrols in the southern Persian Gulf.

Three Iranian fast attack craft and one ship, the Harth 55 class Shahid Nazeri, a 180-foot twin-hulled support vessel, followed the USCG Island-class patrol cutters USCGC Monomoy (WPB-1326) and USCGC Wrangell (WPB-1332), according to U.S. Navy officials.

The Harth 55 repeatedly approached the U.S. vessels’ bows at an unnecessarily close range, including crossing the bows of both the Wrangell and the Monomoy at a 70-yard closest point of approach (CPA).

The Harth 55 approached Wrangell’s bow with vigor, causing Wrangell to navigate to avoid collision while blasting the ship’s horn five times.

The crews of the two USCGC ships sent “multiple alerts” to the Iranians over open radio channels in addition to sounding the bell. According to the U.S. Navy, the IRGCN vessel replied to bridge-to-bridge radio questions, but it’s unclear how these communications went. Regardless, the Harth 55 resumed its “unsafe and unprofessional” maneuvers.

The IRGCN vessels maneuvered away from the U.S. ships and opened space between them about three hours after the U.S. first issued warnings and began defensive maneuvers.

The acts of the IRGCN were considered dangerous and unprofessional. Their actions increased the risk of miscalculation and collision, violated the internationally recognized Convention on the International Regulations for the Prevention of Collisions at Sea (COLREGS) “rules of the road,” and violated the international law obligation to act with due regard for the safety of other vessels.

“U.S. naval forces continue to remain vigilant and are trained to act in a professional manner, while our commanding officers retain the inherent right to act in self-defense,” the U.S. Navy release concluded.

The USCGC ships are part of Patrol Forces Southwest Asia (PATFORSWA), the largest U.S. Coast Guard unit outside the United States, and are part of Task Force 55 of U.S. Naval Forces Central Command.

Given how little time the vessel seems to spend at sea, the arrival of the Shahid Nazeri, which was officially commissioned in 2016, is noteworthy in and of itself. The catamaran did take part in a Russian-Iranian naval exercise earlier this year, at least in part.

The U.S. Navy said the Harth 55 class Shahid Nazeri is a larger catamaran-style, high-speed design with a helipad on top of its rear deck and a 20mm cannon.

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