Operation Tracer was a secret Second World War Royal Navy military operation in Gibraltar, a British Overseas Territory and military base. The impetus for the stay-behind plan was the 1940 scheme by Germany to capture Gibraltar, code-named Operation Felix. Operation Tracer was the brainchild of Rear Admiral John Henry Godfrey, the Director of the Naval Intelligence Division of the Admiralty.

Lord Airey's Battery is an artillery battery in the British Overseas Territory of Gibraltar. It is located near the southern end of the Upper Rock Nature Reserve, just north of O'Hara's Battery. It was named after the Governor of Gibraltar, General Sir Richard Airey. Construction of the battery was completed in 1891. 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 by 1900. The gun at the battery was last fired in the 1970s. In 1997, it was discovered that Lord Airey's Shelter, adjacent to Lord Airey's Battery, was the site chosen for a covert World War II operation that entailed construction of a cave complex in the Rock of Gibraltar, to serve as an observation post. The battery is listed with the Gibraltar Heritage Trust.