An American destroyer was forced to alter its course when approached in an “unprofessional” and “provocative” manner by a vessel belonging to the Iranian Islamic Revolutionary Guard in the Persian Gulf on Monday.

A fast-attack craft belonging to the elite Iranian military group came within one thousand yards of the USS Mahan with its weapon systems manned, according to defense officials.  The Mahan responded by attempting to engage in bridge to bridge communications with the vessel to no avail, followed by launching flares intended to warn the smaller Iranian ship away.

Despite the USS Mahan’s repeated attempts at communicating with the Iranian vessel, they were ultimately forced to alter their course in order to avoid a collision with the smaller ship.

This is far from the first such interaction between fast-attack boats belonging to the Iranian Islamic Revolutionary Guard and U.S. Naval vessels.  In fact, the USS Mahan itself was involved in more than one similar altercations within the past year.

In January, the Mahan and two other accompanying vessels were approached repeatedly by five fast-attack boats belonging to the Revolutionary Guard.  After making repeated attempts to engage in radio communications, followed by using flares and whistles to warn them away, the Mahan ultimately was forced to fire three warning shots across the bow of one of the Iranian boats as it came within 900 yards or so of the ship.

In August of 2016, the Mahan; the USS Makin Island, an amphibious assault ship; and the USNS Walter Diehl, a replenishment oiler, entered the Strait of Hormuz that divides the Persian Gulf from the open ocean.  As they entered the strait, they were shadowed by an Iranian Naval vessel, though such shadowing is considering perfectly normal when traversing waterways near to a nation’s coastline.

However, they were also approached repeatedly by four small attack craft over the nine hours it took to pass through the waterway, ultimately resulting in the Mahan being forced to fire warning shots as one attack-boat came within 500 yards of the ships traveling at a rate of speed that was considered aggressive.

Commander Bill Urban from the U.S. Central Command said the Mahan established radio communications with the four crafts from Iran’s Islamic Revolutionary Guard and “issued multiple radio and visual warnings to remain clear.”