Tamir Kalifa for The Boston Globe

Boston Light

By Billy Baker Globe Staff

LITTLE BREWSTER ISLAND – Last summer, a Coast Guard officer was taking a tour of Boston Light, when a particular artifact caught his eye.

There are a lot of old things at Boston Light – home of the nation’s first and oldest light station, built in 1716 a mile off the coast of Hull – but one artifact seemed particularly old in a particular way.

The item in question was a 293-year-old fog cannon, which for the first 150 years of its life was fired every 30 minutes during periods when poor visibility limited the reach of the light. The officer, Captain James McPherson, wondered if it might just be the oldest artifact in the entire Coast Guard.

Thus began a historical mystery hunt, as Coast Guard historians and archivists worked to answer that question and others, such as making sure the long black cannon on display was the original, and that it had always been owned by one of the entities that would form into the Coast Guard.

After a few months of work, it was determined that McPherson’s hunch was right. The signal cannon was purchased by the Lighthouse Service, which later became part of the Coast Guard, in 1719, making it the oldest known artifact by several decades. The lighthouse itself is older by three years, but was torched by the British as they left town on what is now known as Evacuation Day, March 17, 1776.

“Sometimes maritime historians have a lot of debate over firsts and lasts and whens, but there was quick concurrence from everyone involved in this,” said Lt. Joe Klinker,the public affairs officer for the First Coast Guard District.

On Friday, Rear Admiral Daniel Abel, First Coast Guard District commander, visited Boston Light to see the cannon and present a commendation to Sally Snowman, the 70th lighthouse keeper at Boston Light and the first female.