The tower was built in 1494 as part fortifications and as a home to the governor of Portsmouth. In 1584 it was converted to a gunpowder store, the governor moving residence next to the Garrison Church. At the time of the royalist surrender of Portsmouth at the end of the Siege of Portsmouth during the English Civil War 1200 barrels of gunpowder were stored in the tower. The royalists were able to use the threat of detonating the store as a bargaining chip during the negotiations leading up to the surrender. In 1779 it was converted to a Royal Navy meat store until 1850, when this function was moved to Gosport. The tower was manned during World Wars and was purchased by Portsmouth City Council in 1958-1960.