The first shots of the American Revolution were fired in Massachusetts in April of 1775, more than a year before the thirteen colonies declared their independence. Connecticut needed fortifications to defend the colony from British attack, and in November the colonial government authorized construction of forts on both sides of the Thames River to protect New London Harbor.
The original Fort Trumbull, built just north of this fort, was named after the colony's governor, Jonathan Trumbull. The fort built on the other side of the Thames was named after the deputy governor, Matthew Griswold. Fort Griswold still stands across the river in Groton.
The first Fort Trumbull was designed to repel a naval attack, with earth-and-sod walls sixteen feet thick facing the harbor. The fort lacked such solid protection on the landward side, which proved to be its downfall.
On September 6, 1781, six weeks before the end of the war, a British fleet under the command of the traitor Benedict Arnold approached New London Harbor. About eight hundred, soldiers landed on each side of the river, approximately two miles south of this site. Of those who landed on the left bank of the river, five companies marched on Fort Trumbull from the rear, and the rest proceeded with Arnold to New London, which they burned.
Being outnumbered and without earthen walls or cannon facing the land approach, Captain Shapley and twenty-three men, the patriot force at Fort Trumbull, retreated across the river to join the defense of Fort Griswold. The British then occupied Fort Trumbull and began to fire on Fort Griswold, which was already under attack from the British troops who had landed on the east side of the river.
After hard fighting, Fort Griswold succumbed to the British forces. Colonel Ledyard, American commander of both forts, surrendered his sword, but the British showed no mercy. They slaughtered Ledyard and more than eighty of his men.
As president of the new nation, George Washington urged Congress to authorize fortification of the seacoast in 1794. Fort Trumbull was repaired and reconfigured in the 1790s under this federal fortification program, known as the First System.