The Spanish built an adobe battery called Castillo de San Joaquin at the top of Fort Point to defend the bay with eight brass cannons. Cannon shots were fired from there as a warning or a greeting as ships entered the San Francisco Bay. When a cannon is fired at a distance, you would first see smoke, and seconds later you would hear the boom. If you remember your high school science and the rule about lightning and thunder, you’d say, of course, I knew that. I had the chance to experience live cannon fire as I watched two tall ships during a commemoration sail celebrating Captain George Vancouver’s explorations aboard the sloop Discovery.