| Operation Tracer | |
|---|---|
Stay Behind Cave | |
| Part of Military history of Gibraltar during World War II | |
| Upper Rock Nature Reserve, Gibraltar | |
 Main room of Operation Tracer's Stay Behind Cave | |
 View over the Bay of Gibraltar through observation slit at west observation post of Operation Tracer | |
  Operation Tracer | |
| Coordinates | 36°07′29″N 5°20′36″W / 36.1248°N 5.3432°W |
| Site information | |
| Controlled by | Ministry of Defence |
| Open to the public | No |
| Site history | |
| Built | 1941–1942 |
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.
In 1941, Godfrey decided to establish at Gibraltar a covert observation post that would remain operational even if Gibraltar fell to the Axis powers. Movements of enemy vessels would be reported to the United Kingdom. Godfrey requested the assistance of several distinguished consultants to bring the plan to fruition. The plan was so secret that Godfrey held meetings with his consultants at his private residence rather than at Whitehall.
The decision was made to construct the post using the tunnel system for Lord Airey's Shelter, the underground military headquarters just north of Lord Airey's Battery. The artillery battery was located at the upper ridge of the Rock of Gibraltar, near the southern end of what is now the Upper Rock Nature Reserve.
Construction began in late 1941 and was complete by the late summer 1942. The chambers served as a dual observation post, with an observation slit overlooking the Bay of Gibraltar and a larger aperture over the Mediterranean Sea. Six men were selected for the operation: an executive officer as leader, two physicians and three wireless operators. The men had volunteered to be sealed inside the cave should Gibraltar fall to a foreign power.
The men understood that they would remain sealed in the cave for about a year, although it could be much longer, and provisions for a seven-year stay were stored. The plan was aborted and the Director of Naval Intelligence ordered that the provisions in the complex be distributed and the cave sealed. Rumours of a secret complex, eventually dubbed Stay Behind Cave, circulated for decades in Gibraltar, until discovery of the chambers in 1997 by the Gibraltar Caving Group. The authenticity of the site was confirmed by one of the builders in 1998 and a decade later by one of the physicians, the last surviving member of the Tracer team, who died in 2010.