Washington ? A morning of remembrance turned into one of flashbacks, fear and media missteps Friday when a Coast Guard exercise — unfolding near Pentagon ceremonies marking the Sept. 11, 2001, anniversary — was mistaken as an attack. The false reports of gunfire on the river briefly spooked the capital, sending FBI agents to the scene and grounding flights.

The episode left the Coast Guard promising to “take a good hard look at what we did here today” and military families sore that officials would simulate a confrontation on the Potomac River on a day of raw emotions and high security.

But the exercise, involving speeding boats and at least one helicopter, probably would have passed unnoticed except that two TV networks confused simulated chatter over a Coast Guard radio for actual events and reported that the Coast Guard had opened fire on a suspicious vessel near ceremonies attended by President Barack Obama.

A chain of errors on television and online raised fears the capital might be under assault eight years to the day — almost the moment — after the terrorist attack on the Pentagon. CNN reported 10 shots had been fired, based on information it heard over the network’s police scanner.

After the Reuters news agency reported on what CNN was saying, Fox News followed suit, telling viewers: “Here is what we are learning. The U.S. Coast Guard ship of some type fired on what is considered a suspicious boat in the Potomac River.”

Anchor Bill Hemmer said: “I can’t recall a time or moment like this, on an American river, where the Coast Guard has opened fire.”

In fact, no shots were fired and there was no trouble on the river.

The Coast Guard’s chief of staff, John Currier, said participants in the exercise were given simulated instructions by radio to fire 10 rounds, and someone said “bang, bang, bang” — the routine signal of compliance in drills that don’t involve live fire.

Unaware that it was an exercise, CNN opened its reporting on the incident by saying at least one boat was intruding in a security zone on the river and the Coast Guard was chasing it.

Currier said no apology was necessary for conducting a routine drill. Still, he said, “we’re going to take a good hard look at what we did here today and ensure that if we need to modify procedures, if we need to modify notification, we will do so in the future.”