U.S. military officials say an Iranian drone harassed and nearly collided with a Navy attack jet Tuesday as it prepared to land on an aircraft carrier in the Persian Gulf.

The drone approached the F/A-18E Super Hornet as it circled above the USS Nimitz, officials said. The Hornet’s pilot was forced to make a sudden maneuver to avoid striking the unmanned aircraft, and they passed within 100 feet of each other.

U.S. military officials identified the drone as an QOM-1, raising some question as to whether an aircraft with that designation exists in the Iranian inventory. “The Iranians call it the Sadegh-1,” Cmdr. Bill Urban, a Navy spokesman, later clarified. It can carry two weapons, he said Wednesday, though this one was unarmed.

Takeoffs and landings at sea are inherently dangerous under normal circumstances, requiring extreme concentration and precision to avoid calamity. Tuesday’s incident, which U.S. officials said occurred in international airspace, is an unsettling development for that reason, and it marks the latest threatening encounter between the two militaries.

In a statement, the U.S. Central Command declared the incident “unsafe and unprofessional,” calling it a breach of international maritime customs and laws. It’s the Navy’s 13th such run-in with Iranian military forces this year, officials said.

It’s unclear whether Iranian military officials communicated with the Americans, who say they made repeated radio calls warning the drone’s operator to keep away. Officials at Centcom’s headquarters in Tampa declined to address follow-up questions.

The Super Hornet belongs to Strike Fighter Squadron 147, which is deployed aboard the Nimitz from Naval Air Station Lemoore in California. The Nimitz is homeported in San Diego.

The Nimitz’s crew detected the drone hours earlier as it loitered a few miles away, an unidentified Defense Department official told Military Times. When the encounter occurred, the Hornet’s pilot performed a rollover to avoid striking it, the official said.

Tuesday’s close call probably set off a flurry of activity aboard the ship and within the cockpit of every other U.S. aircraft aloft nearby, said Amy McGrath, a retired Marine Corps officer who piloted F/A-18s throughout her career. That the incident ended smoothly highlights how skilled and disciplined American combat pilots are and the extensive training they undergo to prepare for such a contingency, she said.

Operating from aircraft carriers, McGrath said, is “enormously dangerous” even under normal conditions. “You have to be 100 percent in it, physically and mentally,” she told The Washington Post. “It requires so much focus.”

Before every mission, all pilots consult a checklist on the procedures for a midair collision — with anything, McGrath said. A bird. Another aircraft. Even a drone. “You just try to avoid whatever it is coming at you in the safest manner possible and save the aircraft,” she added. “It’s instinct.”

In recent months, U.S. jets operating in Syria have shot down armed Iranian drones that moved too close to American ground troops. And there have been numerous close calls involving U.S. and Iranian vessels at sea.

This latest encounter comes two weeks after the crew of a Navy patrol boat fired at an Iranian military ship that had come within 150 yards of the Americans as they trained in the Persian Gulf.

Such run-ins are becoming more frequent. Last year, the Pentagon documented 35 hostile interactions with Iranian forces, up from 23 in 2015.

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