Initially known as St. George's Tower, it was constructed in the late 18th century on the order of then Lieutenant Governor Charles O'Hara, under the presumption that it would be useful in observing the enemy at the Port of Cadiz.

[1][2] O'Hara's Tower was in Gibraltar, the British Overseas Territory at the southern end of the Iberian Peninsula.

[13][14][15] O'Hara had been of the opinion that a tower at The Rock's summit would enable the garrison to observe the activity of the Spanish fleet at the Port of Cadiz, about 60 miles (97 km) away.

The men of HMS Wasp adjusted their guns such that they were able to target at a high elevation, and brought down the tower with their sixth shot.

Following demolition of the tower, O'Hara's Battery was constructed on the same site, with the first 6-inch breech-loading gun installed on a Vavasseur mounting in 1890.