Way to go CNN. USA Today has the timeline of events, for what turned out to be a radio-only exercise:

CNN is reporting that the Coast Guard has fired on a boat on the Potomac River. Update at 10:10 a.m. ET: The report of some activity on the river comes only minutes after President Obama concluded 9/11 memorial ceremonies at the Pentagon not far away. Update at 10:12 a.m. ET: CNN says the Coast Guard fired 10 rounds at the boat. Update at 10:14 a.m. ET: CNN broadcasts what it says is audio of the Coast Guard apparently speaking to a suspicious boat. The Coast Guard speaker is heard saying; “Slow down or you will be fired on.” Update at 10:27 a.m. ET: The AP quotes the Coast Guard as saying training was being conducted in Potomac River moments before Obama motorcade crossed. Update at 10:30 a.m. ET: CNN quotes two police sources as saying the incident was a possible Coast Guard training exercise. Update at 10:32 a.m. ET: Fox News quotes Coast Guard Chief Keith Moore as saying no shots were fired as part of the exercise. Update at 10:33 a.m. ET: Reuters quotes an FBI spokeswoman as saying the agency was told by the Coast Guard that no shots were fired at a boat in the Potomac. Update at 10: 41 a.m. ET: NBC’s Pete Williams, quoting a “senior Coast Guard official,” says the incident was just an exercise to “challenge response times.” Williams says the exercise was strictly a “radio exercise” and did not involve any boats or any firing by the Coast Guard. Williams reports that a “citizen” overheard the radio exercise and passed that along to some news organizations, which broadcast reports of possible shot being fired. Update at 10: 53 a.m. ET: USA TODAY’s Kevin Johnson reports that the Coast Guard say that no shots were fired and that the incident involved a “radio exercise.” Johnson says the Coast Guard is preparing a statement for release in a few moments, which we will carry.