cannon booms and foreign flags

Another unexpected view from my balcony - Saturday morning I looked out and saw a strange, unfamiliar flag flying over the old fort.  It was bright red with a small union jack in the upper left corner.  I don't know what time in history the flag was from but I'm guessing there was a re-enactment going on at the fort because later I heard several loud booms as cannons were shot off. I'm assuming they were firing blanks because I didn't see any cannon balls zooming across Spy Run or splashing into the river. That would have been something to see though.