Civil-war era cannons overlook the harbor at the Fort McHenry National Park. In the distance you can see the Key Bridge. It was close to the bridges' left span that Key was a witness to the battle on a British ship anchored about 8 miles from Ft. McHenry. A small red white and blue buoy marks the ship's estimated anchorage.
This video gives a great story on the battle on Baltimore. It is ironic that had the moon and tides been different in September 1814, the British might have sailed out of the Chesapeake Bay after burning Washington, without attacking Baltimore, and continued to rain terror on the Virginia and Carolina coast line enroute to New Orleans. FN Vogel p.269-270