After the battles of Lexington and Concord in 1775, British supplies were running low.
British soldiers went on Grape Island, home to a privately owned farm, to pilfer hay for their horses and cattle to feed their men. The local farm owner Elisha Leavitt, a Loyalist, generously offered tons of his hay to the army while the patriots watched in vain from shore, unable to launch their boats until high tide came in. The patriots did finally make it onto the island, forcing the British off, and in retribution burned the remaining hay supplies and the barn to the ground.
In their words from the Rivington's Gazetteer. June 8, 1775
"The soldiers and sailors immediately left the barn, and made for their boats, and put off from one end of the island, whilst our people landed on the other. The sloops hoisted sail with all possible expedition, whilst our people set fire to the barn, and burnt seventy or eighty tons of hay, then fired several tons which had been poled down to the water side, and brought off the cattle."
The incident came to be known as “The Grape Island Alarm.” A granite memorial to the incident can be found at Webb Memorial Park on the mainland across the water from Grape Island.