From a plaque at Conanicut Battery:
"In the early 1770's - even before the Declaration of Independence - Narragansett Bay was the scene of frequent confrontations between the British Navy and Rhode Islanders. The British aggressively enforced their increasively expensive custom duties and the Rhode Islanders aggresively resisted the British.
In 1772 a group of Providence rebels captured and burned the HMS Gaspee. In 1773 the HMS Rose and 14 other warships shelled Bristol, while British naval forces regulary raided the coast and local shipping for food and supplies. In August 1775 the Rhode Island General Assembly had most of Jamestown livestock removed to relative safety of South Kingston. Around this same time Jamestown resident John Eldred, it is said, placed a cannon between two boulders overlooking East Pasge and fired occasionally at British ships passing by. On December 10-11, 1775, British mariners raided the small village at Jamestown. They burned almost all the houses along Narragansett Avenue, made off with available livestock, and effectively drove much of the population away.
The calamitous December raid, and realization that control of Conanicut Island could mean control of the bay, caused the colony to begin fortifying the island.
In January 1776 the General Assembly ordered 300 militiamen to Jamestown and, in May, voted to "employ a sufficient number of men to erect a fort at Beaver Tail, upon Conanicut to contain six or eight heavy canons". Shortly thereafter, on this site on Prospect Hill, troops erected an earthen gun battery with a commanding view of West Passage. The battery, probably crescent-shaped, took advantage of both height and slope of the terrain."
Good footnote. Thanks!