Fort Independence, Boston Harbor

Fort Independence was also once on its own island, long before Boston extended tentacles out into the harbor to anchor it solidly to the mainland. In one form or another, this site has been fortified for nearly 400 years, practically since the founding of Boston, though for the last fifty years it has been a historical park rather than an active military site. I was surprised to learn that one of its later duties was as a naval degaussing station: apparently, ever since World War II, degaussing has been an important part of defending ships against magnetic mines and other systems that work based on magnetic signature. Learning about this, it makes sense---these are big magnetizable steel objects that move themselves constantly through magnetic fields---but to me it's also another wonderful reminder of how apparently abstract physics reaches out and touches our lives through unexpected windows.