The US Navy ship saw that an Iranian patrol boat tried to be in close vicinity of USS Thunderbolt. A number of warning signals were given which were ignored by the Iranian patrol boat and it reportedly urged the US Navy to fire in the water as a final warning.
According to CNN, a Navy ship of the US was forced to fire warning shots after an equipped Iranian patrol boat tried to get close to the northern ending of the Persian Gulf. A defense official said that the Iranian boat was driven by the Iranian Revolutionary Guard Corps. The shots were fired because the boat came within 150 yards of the USS Thunderbolt, a US Navy's patrol ship. During the incident, the USS Vella Gulf was present along with the USS Thunderbolt and two US Coast Guard vessels were present in the region as well.
Before firing the warning shots, many warnings were given to the Iranian patrol boat, but they didn't react to any of them. There are few internationally recognized communications which are meant to show that there is a danger and these communications include flares firing, five small blasts and radio calls.
Before firing the actual warning shots, the US ship tried to communicate the danger in all the above-mentioned ways. And, it was due to a possibility of collision that the Navy ship finally fired up warning shots in the water. It was after then the ship stopped its movement towards the USS Thunderbolt but reports claim that it still kept lingering in the region for the next couple of hours.
The defense officials further said that there were many US Navy ships which were present in the incident area at that time. However, Iran's Revolutionary Guard claimed that it had foiled the provocative movement of US warship towards the Navy Patrol of Iran. The tension between both the countries has always been there in the Gulf of Persia.