The entrance to the tunnel would be bricked up, thus sealing the six men in the cave for a maximum of 7 years.
After the end of the Second World War, a myth arose that there was a secret walled room in the Rock of Gibraltar that was intended for six men to live in during the war. It was expected that in the case of the capture of Gibraltar by the Nazis, their task would be to monitor German activities for at least one year.
Later, it turned out that the subject of this rumor was the operation codenamed “Tracer.”
In 1940, Germany had a plan codenamed Operation Felix according to which German troops would go through Spain to capture Gibraltar. It was an offshoot of the larger plan with which Germany hoped to cut off Great Britain from the rest of the British Empire.
Operation Felix became the catalyst for the development of the British plan codenamed Operation Tracer.
In the summer of 1941, Rear Admiral John Henry Godfrey, the Director of the Naval Intelligence Division of the British Admiralty, created plans for a secret observation post in Gibraltar, which would remain operational should Germany seize Gibraltar.
The plan was classified, and very few people knew about it.
During the US War of Independence in the 18th century, and later during World War II, the British dug a tangled maze of tunnels at the base of a 426-meter (465-yard) high monolithic rock located in the southern part of the Iberian Peninsula. The purpose of the maze was to protect the strategically important object from enemy attacks.
The total length of all the tunnels was about 50 kilometers (31 miles). In the past, they had been used to store weapons. The also contained hangars, barracks, warehouses with supplies, and a hospital.
These tunnels were chosen as the location for Operation Tracer. An observation post would be created and equipped. Soldiers would be placed within the post and, using secret radio communications, they would inform the Admiralty about the movements of enemy ships.
The initial plan included placing five people inside for a period of one year and providing them with all the necessary food. However, this was then changed to placing six people in the rock and providing them with provisions for a period of seven years. Godfrey held a series of consultation meetings with experts on the feasibility of this scheme.
George Murray Levick, the Royal Navy Surgeon Commander, was one of the consultants on Operation Tracer. He was called out of retirement as a consultant for survival, staff psychology, diet, clothing, exercise, ventilation, and handling dead bodies. In addition, Levick lived with the Tracer team during the rehearsal.
Thomas Horder, 1st Baron Horder, was consulted on medical matters. Prior to this role, he had been the doctor to both monarchs and prime ministers. Colonel Richard Gambier-Parry advised on the communication aspect of the operation.
Construction of the secret complex began in late December 1941. The tunnel works were carried out under the strictest secrecy. None of the workers knew about the operation and, upon completion of the work, they were all immediately returned to England.
The room in which the men were supposed to live was 57,600 cubic feet (1,630 cubic meters) with dimensions of 45 ft x 16 ft x 8 ft (14 m x 4.8 m x 2.4 m). It was located at an elevation of 1,350 feet (410 meters).
Two observation openings providing ventilation: one faced east over the Mediterranean Sea while the second faced west over the Gulf of Gibraltar. There was also a small radio room which contained equipment for wireless communications, including an HRO Receiver and a Mark 3 transmitter.
The room had a water tank with a capacity of 10,000 imperial gallons (45,000 liters). Three 12-volt 120-ampere batteries were provided, to be charged using one of two generators, powered either by a bicycle or hand-cranked.
The bicycle additionally set in motion the ventilation system. Its chain was replaced by a leather belt in order to reduce noise.
For the purposes of additional communication, an external rod antenna 18 feet (5.5 meters) was recommended. The antenna would be hidden in a pipe that went down the stairs to the main room.
Staff had the opportunity to climb out onto the platform and get some fresh air because the holes and ledges were quite large. Not far from the center of the main staircase was another one leading to the western observation point. A concrete wedge hid the western viewing slot.
To reduce sound transmission, the entire main chamber was plastered and the floor was covered with cork tiles. The entrance to the tunnel would be bricked up, thus sealing the six men in the cave.
At the end of April 1942, a team was formed for Operation Tracer. This included three telecom operators, two lieutenant-surgeons (Bruce Cooper and Arthur Milner), and a senior officer as a team leader.
However, the leader soon had to be replaced, probably because of his refusal to participate with three ordinary soldiers who were to serve as radio operators. The names of the three radio operators are unknown. The replacement for the original leader was “Windy” Gale, a native of Kent.
By early August, a Pathfinder team was formed to provide cover for their stay in Gibraltar. At the end of the month, the construction of the cave was almost completed, and the supplies were already in place.
However, Operation Tracer was never carried out. On August 17, 1943, the Allied forces defeated the troops of the Axis countries located in Sicily and captured the island. After that, the threat to Gibraltar became insignificant.
On August 24, 1943, the Director of Military Naval Intelligence sent a secret message in which he ordered the men to conduct one last lot of wireless exercises, block up the caves, and distribute supplies.
After World War II, rumors about a secret room in the Rock of Gibraltar appeared. For many years, enthusiasts explored tunnels and caves but could not find any solid confirmation to back up this story.
However, in December 1997, the Gibraltar Caving Group discovered a secret complex in Upper Ridge at the southern end of the Upper Rock Nature Reserve. It soon became clear that this place was directly related to Operation Tracer.
The Gibraltar Group discovered a walled-up section. Removing a few bricks, they found a doorway beyond which they discovered observation points and the remnants of a bicycle.
Former telegraph operator Dennis Woods in September 1998 said that he played an important role in the construction of this facility. He also stated that there were other tracker groups in Gibraltar, but his group was the main one. Woods suggested that the Tracer units worked during the Suez crisis.
In April 2012, the documentary Operation Tracer – Stay Behind Cave was broadcast. There are also plans to make a feature film based on the history of Operation Tracer.