The Battle of Groton Heights (also known as the Battle of Fort Griswold, and occasionally called the Fort Griswold massacre) was a battle of the American Revolutionary War fought on September 6, 1781 between a small Connecticut militia force led by Lieutenant Colonel William Ledyard and the more numerous British forces led by Brigadier General Benedict Arnold and Lieutenant Colonel Edmund Eyre. Lieutenant General Sir Henry Clinton ordered Arnold to raid the port of New London, Connecticut, in an unsuccessful attempt to divert General George Washington from marching against Lord Cornwallis's army in Virginia. The British fleet anchored about 30 miles west of New London to make final preparations, and then sailed for New London late on September 5, intending to make a nighttime landing. However, contrary winds prevented the transports from reaching the port until it was already daylight on September 6. Upon receiving the alert, Ledyard sent a messenger to notify Governor Jonathan Trumbull and local militia leaders of the British arrival, and went to Fort Griswold to arrange its defenses. Fort Griswold's guns were fired twice, a signal of enemy approach. However, one of the British ships fired a third round, changing the meaning of the signal to indicate the arrival of a victorious friend. This signal confusion led to delays in mustering militia companies.

On the return of the second parley flag, Eyre launched a full-scale assault upon the fort and its roughly 150 defenders. As the British neared the ditch, they were met by a bombardment of grapeshot that killed and wounded many. This briefly scattered them, but they reformed into two units. Eyre led one force against the southwest bastion, where American fire repulsed the assault, seriously wounding Eyre and several of his officers. A black soldier named Lambert Latham is credited with killing the British officer who killed Colonel Ledyard. British descriptions of the battle ascribe several possible reasons for their behavior. During the battle, the fort's flag was allegedly shot down at one point, although it was quickly re-raised. Some of the British attackers claimed to have interpreted the event as striking the colors, making a sign of surrender; the British suffered significant casualties when they then approached the fort on that occasion. They claimed that this led them to disregard Ledyard's legitimate surrender, and they vented their anger over the death and wounding of their commanding officers. The massacre at Fort Griswold marked one of the largest tragedies in the history of Groton and Connecticut, and was one of the last British victories in North America before the end of the war.