O'Hara's Battery is an artillery battery in the British Overseas Territory of Gibraltar. It is located at the highest point of the Rock of Gibraltar, near the southern end of the Upper Rock Nature Reserve, in close proximity to Lord Airey's Battery. It was constructed in 1890 at the former site of a watchtower that had earned the name O'Hara's Folly. The battery and tower were both named after the Governor of Gibraltar Charles O'Hara. The first gun mounted on the battery was a 6-inch breech loading gun, which was replaced with a 9.2 inch Mark X BL gun in 1901. The battery was in use during World War II and was last fired during training exercises in 1976. O'Hara's Battery has been refurbished and is open to the public. The battery and its associated works are listed with the Gibraltar Heritage Trust.

The Rock of Gibraltar is a highly strategic monolithic limestone mountain 426 m (1,398 ft) high dominating the western entrance to the Mediterranean Sea. It is situated near the end of a narrow 9 kilometres (5.6 mi) long promontory stretching due south into the Mediterranean Sea and is located within the British territory of Gibraltar, and is 27 km north-east of Tarifa, Spain, the southwestern tip of Europe on the Iberian Peninsula. The rock serves as an impregnable fortress and contains a labyrinthine network of man-made tunnels known as the Tunnels of Gibraltar. Most of the Rock's upper area comprises a nature reserve which is home to about 300 Barbary macaques. It is a major tourist attraction.