Last Thursday, an American surveillance ship, the USNS Invincible, had a run-in with Iranian Naval frigate that U.S. officials characterized as “unprofessional.”  The ship was then harassed by Iranian vessels once again on Saturday, forcing it and the British ships it was accompanied by to change course to avoid a collision.

The USNS Invincible is an unarmed surveillance ship equipped with sonar, designed to monitor submarine activity as well as radar to track surface missile launches, similar to the Russian vessel seen off the coast of the United States in recent weeks.  Last Thursday, an Iranian naval frigate came within a hundred and fifty yards of the American ship in the Gulf of Oman, just south of the strategic Strait of Hormuz.  The interaction between the two vessels was deemed “unprofessional” but not unsafe, as the frigate maintained a course that was parallel to that of the Invincible and didn’t pose a direct threat to the safety of those on board.

The USNS Invincible courtesy of the US Navy

Iranian fast-attack boats set their sights on the Invincible once again on Saturday, this time however, their conduct has been labeled both “unprofessional” and “unsafe” as the boats positioned themselves directly in the path of the larger American vessel, as well as three British Navy ships traveling in formation with the Invincible.

The four ships were forced to alter their course in order to avoid a collision with the Iranian crafts.  The fast attack boats were manned by members of Iran’s elite Revolutionary Guard.

In January of this year, the crew of the USS Mahan were forced to fire warning shots at similar fast attack boats from the Iranian Revolutionary Guard.  The interaction, which took place within the Strait of Hormuz, involved the fast attack boats closing in on the Mahan at a high rate of speed.  Although they were still approximately 900 yards out from the ship when it fired, their trajectory and rate of speed was deemed threatening enough to warrant the use of the warning shots – an uncommon event between the two naval forces.

According to reports, the Mahan made repeated attempts to contact the Iranian ships as they closed in on them, with those communication attempts transitioning into warnings as the Mahan used floating smoke grenades to further deter the Iranians.  The ship also used a siren and its whistle to draw the attention of the smaller vessels as they continued their rapid approach, to no avail.  When none of those efforts succeeded, the Mahan fired three warning shots, which immediately prompted the Iranian vessels to change course and make radio contact with the American ship.

“Disregarding the warnings, the IRGCN vessels continued to directly approach Mahan at a high rate of speed. Mahan then fired three warning shots with a crew-served 50 caliber machine gun, and the IRGCN vessels arrested their high-speed approach,” a Navy official told CBS News at the time.

“Naval Forces Central Command assesses this interaction as unsafe and unprofessional due to the IRGCN’s vessels high-speed approach on Mahan with weapons manned and disregard for repeated warnings via radio, audible siren, and ship’s whistle,” the official added.