Multiple fast attack boats of the Navy of the Army of the Guardians of the Islamic Revolution, popularly called the Revolutionary Guards' Navy (NESDA), last March 4 harassed a U.S. Navy spy ship keeping track of Iranian ballistic missile launches.
The incident involved the USNS Invincible (T-AGM-24), which is classified as a tracking ship operated by the Military Sealift Command, as she was transiting the Strait of Hormuz escorted by three minesweepers of the Royal Navy.
The rapid approach of the NESDA boats forced the Invincible and her escorts to alter course away from the Iranians. The Iranian squadron came as close as 550 meters to the Invincible, said the U.S. Navy.
The navy said attempts were made to talk to the Iranians over radio, but there was no response. It characterized the incident as "unsafe and unprofessional."
Invincible deployed to the Persian Gulf in 2012, passing through the Straits of Hormuz in convoy with Royal Navy minesweepers.
The Invincible is officially classed as a "missile range instrumentation ship" whose job it is to monitor missile launches and collect data. This job description makes the Invincible a high tech spy ship, which is in the Persian Gulf to spy on Iran's continuing series of ballistic missile launches.
As a missile range instrumentation ship, the Invincible carries the Cobra Gemini dual band (X-band and S-band) radar developed by the U.S. Air Force to gather data on theater ballistic missiles launched by countries of interest such as Iran.
The dual frequency Cobra Gemini is designed to collect precise scientific and technical intelligence (S&TI) data about medium range ballistic missiles such as those operated by Iran.
In late January, Iran test-fired a medium-range ballistic missile, which was the first launch of its kind since Donald Trump took office.
The launch was a failure after the missile flew more than 500 miles before crashing, according to U.S. officials.