In 1781, a Spanish fleet sailed into Pensacola Bay right past the British guns of the Royal Navy Redoubt at Fort Barrancas. The British guns fired but did little damage to the ships, and Pensacola passed into Spanish hands. To remedy this defensive weakness, Spanish construction began in 1793 on a water level battery at Fort Barrancas; Battery San Antonio was completed in 1797. Built of masonry, it held seven guns and three rooms, one of which served as the state prison under Spanish rule. In 1821, Spain ceded Florida to the United States. The Army Corps of Engineers redesigned, enlarged, and repaired Battery San Antonio in 1839, and renamed it the Spanish Water Battery.