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Operation Tracer, Part 1 – Gibraltar’s castle in the sky

To date the primary role (…) has been against threatened attack from Spain across North Front. Owing to changes in the Situation during the past year, a seaborne attack is now considered possible. The primary role (…) has been changed to an anti-tank and anti-landingcraft one.

This extract shows a shift in defencive focus as the situation in North Africa deteriorates and perhaps blind faith in the Royal Navy to secure the sea routes weakens. Taken from Gibraltar 18th Defence Regiment War Diaries, Appendix A, 3 July 1942, National Archives WO 176/194

I think it is fair that a lot has been written about Operation Tracer, but the pool of source information is rather shallow. The single official document in which this operation is mentioned is contained within a once-classified leather-bound volume in the National Archives, ADM 223/464, the Official wartime history of Naval Intelligence and the Naval Intelligence Department, 1939-1942. Authorship of this now authoritative document is credited to author and journalist Charles Langbridge Morgan; his initials C.L.M. adorn many of the articles and indeed C.L. Morgan has been debossed onto the book’s spine. This article will draw heavily on the information contained within this volume, a transcript of which I have made available to download here.

I was also privileged to be able to visit what is being described as the Stay Behind Cave in Gibraltar. This is likely the cave modified and intended for use if the Tracer operation was ever to be required. It was discovered in 1997/1998 by the then Gibraltar Caving Group. I was able to capture rare 360-degree photographs from inside the tunnel system, as well as high-resolution digital images that will form much of my analysis of the tunnels and operation. I will try and only interpret the evidence available, and use contemporary sources to establish more about the concept of operations.

As I am sure. you will gather, this is a complex topic and there is still much more to learn about the deployment of Tracer teams. While I have done considerable research into the topic, I will not always get things right. Please use the form at the bottom of this article if you would like to pass on any feedback or new sources of information that will help change the narrative on Operation Tracer. This article is around 10,000 words and there are lots of images to try and explain and interpret what I found. Let me know if anything needs further work.

What was Tracer?

There are often dramatic words such as internment or entombment used to describe the Operation Tracer mission, and this can sometimes be unhelpful to the historian attempting to establish the facts. The most obvious term that may confuse is the casual reference to ‘Stay-Behind Cave.’ Across mainland Great Britain during the Second World War, a series of auxiliary units were established, “sometimes known as Churchill’s Secret Army, a sabotage organisation set up in 1940 in case of a Nazi invasion.”1The British Resistance Archive,, accessed 28 March 2024 These organisations recruited civilians to undertake surveillance and sabotage against invading forces. They had links to both the Special Air Service (S.A.S.) and Special Operations Executive (S.O.E.) and were offensive, conducting attacks on the enemy and their supply lines. Operation Tracer, on the contrary, was an unarmed Admiralty observation post, reporting solely on shipping movements. There is no evidence they would have had any other mission.

Their purpose was to report shipping movements to the Admiralty by clandestine wireless.

Statement contained in ADM 223/464, pp268-270, TRACER. Download a transcript here.


I have scoured the official record and pulled out confirmed dates to help build up a timeline of events leading to a Tracer team being deployed to Gibraltar.

  • August 1941 – Conception. Technically reported as “late summer” when the idea originated.
  • November 1941 – Cdr. Birley (the Senior Officer (Intelligence (SOI(I)) Gibraltar) wrote a local report on the feasibility. This report identified the use of an existing shelter at Lord Airey’s Battery. A copy of this has not yet been found, but it details construction, camouflage, sanitation, wireless requirements, stores and personnel.
  • Nov/Dec 1941 – Lord Horder, a senior government physician, was consulted. It seems remarkable to take medical advice so early in the planning, but it shows how seriously the plan to isolate a group of men for a year or more was being taken.
  • 27 December 1941 – Col. Coredeaux from the Secret Intelligence Service (M.I.6) issued a detailed report on the feasibility. Engagement with S.I.S. shows that other options may have been considered such as using a network of spies after any invasion. It can only be presumed that, much like the British had done early on in the war, a mass evacuation of the population would have been conducted, potentially removing any spies that were in place.
  • 11 January 1942 – Capt. Sandwith, the Deputy Director of Signals Division, Y-Service, issued a report on Tracer communications.
  • 25 January 1942 – Meeting to discuss Horder and Levick’s report attended by both men as well as John Cordeaux and Ian Fleming. The report was based on Levick’s experience in the Antarctic.
  • 15 February 1942 – Estimated date for radio corridor completion, prompting a communications test as soon as possible afterwards. This would likely have been carried out by a S.I.S. wireless technician using equipment Gambier-Parry already had in Gibraltar.
  • 17 February 1942 – A further meeting was held to discuss Tracer, this time at John Godfrey’s flat, 36 Curzon Street. At this meeting, Lieutenant White was suggested as a potential officer in charge of the party. They also agreed that Levick would be present during the rehearsals.
  • 17 February 1942 – Recruitment begins of one officer as leader of the operation, two doctors and three Royal Navy telegraphists. Lord Horder was tasked with recruiting the doctors. Admiral Whitworth was requested to provide the officer and telegraphists.
  • 1 March 1942 – John Godfrey reported to the 1st Sea Lord about Tracer.
  • 15 March 1942 – Progress report was issued. Reference NID 001107/42. This has not yet been uncovered and is likely lost to time.
  • 30 April 1942 – Two surgeons and three signallers were selected. There is no leader yet, presumably Lt. White was not selected.
  • 16 May 1942 – Training begins at Shotley, the Royal Navy shore training establishment in Sussex.
  • Mid-July 1942 – The anticipated time the team would deploy to Gibraltar.
  • 1 August 1942 – The Tracer team deployed to Gibraltar, falling under the supervision of the new S.O.(I) Pyke-Nott.
  • 24 August 1943 – Final W/T exercise and cessation of operation after a coded message was sent from the Admiralty to Gibraltar.


To build credibility for the many stories that exist, I have tried to track and name every personality associated with Operation Tracer. I will start at the most senior, and work down to the known men who volunteered to take part in the operation. Rank and service at the time of the operation are included, where known.

  • Vice Admiral John Henry Godfrey R.N.2Royal Navy, Director of Naval Intelligence, between February 1939 to November 1942. Godfrey was intimately attached to this operation and was involved in all levels of planning.
  • Lieutenant Commander Ian Lancaster Fleming R.N.V.R.3Royal Naval Volunteer Reserve, personal assistant to Vice Admiral John H. Godfrey. Fleming was reported to be a long-time friend of Godfrey and despite being given far from a basic rank was underqualified for the position. However, he appeared very good at his job and played a key role in many wartime clandestine operations. He later went on to author the James Bond novels and it is thought that Godfrey was his inspiration for the character M.
  • Edward Merrett, personal secretary to Vice Admiral Godfrey.
  • Charles Langbridge Morgan, author and journalist wrote the post-war official history of N.I.D. but otherwise had no role in Operation Tracer. His authorship of the official history could therefore be taken as an objective and impartial summary of the documents and records provided to him.
  • Lieutenant-Colonel John Kyme Cordeaux R.M.4Royal Marines, the Naval Intelligence Division representative within M.I.65Military Intelligence Section 6 the Secret Intelligence Service.
  • Dr. Thomas Jeeves Horder, 1st Baron Horder, consultant physician. He was responsible for selecting the doctors suitable for the operation. He may have known Bruce Cooper personally or selected him from a paper sift. It is believed that Cooper then chose the second doctor, Milne.
  • Colonel Richard Gambier-Parry, Head of Section VIII Secret Intelligence Service. Gambier-Parry was a communications expert and was responsible for the network of S.I.S. communication stations around the world. When the operation was proposed and a site chosen, Gambier-Parry suggested: “training a W/T6Wireless Telegraphy, morse code transmitted over the radio technician at once and meanwhile sending out one of his men to carry out trials on the site with the apparatus (he) already had at Gibraltar.
  • Captain Humphry Sandwith, Deputy Director Signals Division, Y-Service, DDSD(Y), Head of N.I.D. 9. He was responsible for reporting on communications related to Tracer. He consulted with Col. Gambier-Parry
  • Admiral Sir William Whitworth, Second Sea Lord and Chief of Naval Personnel, 1941-1944, was approached to provide personnel for the operation, excluding the doctors. By May 1942 the three Leading Signalmen had been selected, but not yet the executive officer.
  • Surgeon Commander George Murray Levick R.N., Naval surgeon and Antarctic explorer. His knowledge and experience of Antarctic expeditions were invaluable to the planning, in particular, the winter he spent with a small group locked down in their Antarctic hut.
  • Captain ‘Windy’ Gale was reported to be the executive officer of the team. Other than being from Kent, his identity is unknown, and it is unknown if he was a prospective candidate or if he deployed with the team.
  • Commander Geoffrey Birley, Senior Officer (Intelligence) SOI(I) Gibraltar during the initial conception phases. Carried out the first reconnaissance of the Rock and identified a suitable location for the Tracer tunnel. The official history states that “Birley’s report was an elaborate one with appendices on the details of construction, camouflage, sanitary arrangements, wireless requirements, stores and crew.”
  • Commander James Grenville Pyke-Nott, Senior Officer (Intelligence) SOI(I) Gibraltar during the deployment of the Tracer team.
  • Colonel H.M. Fordham, Royal Engineers, Chief Engineer on Gibraltar 19 September 1940 – 14 December 1941. 7 accessed 28 March 2024
  • Lieutenant Colonel Robert Alistair Hay, Royal Engineers, Deputy Chief Engineer on Gibraltar, 19 June 1941 – 16 January 1944.8 accessed 28 March 2024
  • Lieutenant White R.N.V.R. is reported as having been selected for an interview, however, no further mention of him is made suggesting he was not suitable or did not accept the position.
  • Surgeon Lieutenant Dr Bruce Cooper R.N.V.R. was the first doctor to be recruited. He visited the tunnel in 2008, not long before his death, and while initially not recognising the cave later confirmed the newly discovered tunnel system was the one prepared for Operation Tracer.
  • Surgeon Lieutenant Dr. Arthur Milne R.N.V.R. was recruited by his friend Dr. Cooper as the second doctor on Tracer.
  • Mr. Dennis Woods, described in one article as a former telegraph operator9Ruslan Budnik, War History Online, 20 March 2019 is said to have been the plasterer who plastered the main chamber. He signed his name in pencil near one of the doorways.


Although often considered to be a “side show” during the Second World War, the campaign in the Mediterranean and Middle East was one of the most complex, interrelated, extensive, and certainly most enduring theatres of that conflict.

World War II in the Mediterranean and Middle East, Niall Barr
Clifton Utley’s War Map of the Mediterranean area. Gibraltar is on the far left where Spain almost touches Morocco.

The strategic importance of Gibraltar can not be understated. For centuries the British relied on keeping the vital supply lines through the Mediterranean Sea open. Choked at either end by the Straights of Gibraltar and the Suez Canal, Britain had empirical control over Gibraltar, Malta, Cyprus, Egypt and Aden. These outposts enabled the Royal Navy, the largest and most powerful navy in the world at the time, to dominate and ensure trade routes were kept open. As the Axis powers (Germany, Italy, Vichy France) tightened their grip on countries boarding the coastline, maintaining as much superiority of the sea would place a chokehold on these overstretched forces. As well as the world’s naval superpowers engaging in intense engagements, airpower played a huge role in the Mediterranean, with Malta seeing intense and relentless bombardments. Gibraltar also came under sporadic aerial bombing as well as subversive underwater attacks by Italian divers.

Should Spain capitulate or align itself to German objectives, Gibraltar would almost certainly have been overpowered by the land attack, increased aerial bombardment and more than likely a powerful combined naval component. This would have been enacted in Operation Felix, the German plan to take Spain and Gibraltar. This military planning was being undertaken at the same time German diplomats were attempting to find a political solution, but Spain, knowing that any military action would be disastrous to their country, continually declined to permit German incursions. Through a well-established network of spies, it was almost certain Britain was aware of these events right back to late 1940 and 1941.

This was a design by D.N.I. to establish first at Gibraltar and, if possible, in other places such as Malta and Aden, secret observation posts which could be maintained even if the places in which they were situated should fall into the hands of the enemy.

It is no surprise that right at inception naval authorities were considering Tracer style deployments at other key positions in the Mediterranean. ADM 223/464, pp268-270, TRACER. Download a transcript here.


Tunnelling in Gibraltar was a colossal venture in the 1940s, peaking in 1942 with over 35,000 cubic yards of rock being excavated that year alone. Specialist tunnelling companies from the Royal Engineers, including a large contribution from Canadian tunnellers, undertook this work night and day, with excavated rock being used to extend the newly expanded airfield. It was rumoured (uncredited) that German spies observing the work could estimate the scale of tunnels based on the quantity of spoil removed, and from where. Unlike defence construction in Great Britain, everything done in Gibraltar was on show for the enemy to see from the coast of Spain, North Africa, spies in Gibraltar and submarines lurking nearby.

With limited resources and limited time to prepare for Operation Tracer, it is no wonder that an existing tunnelling scheme was identified as suitable for modification to support Operation Tracer. Not only would this expedite the deployment of a team, but it would draw little attention compared to the creation of a new tunnel system with no apparent purpose. The main tunnelling work had likely been completed and all that was required was to fit it out.

A tunnel to support Tracer would first of all need to be well suited to give an excellent unobstructed view over the naval dockyard and facilities on the west side of Gibraltar, and ideally provide a vantage point over the entrance from the North Atlantic. It would need to be large enough to accommodate 6 people, with sufficient food and water for up to a year, as well as power and sanitation. Military engineers in Gibraltar identified a suitable location.

[7] The S.O.(I) Gibraltar, Cdr. Geoffrey Birley had, in company with the Chief Engineer (Col. H.M. Fordham) and his deputy (Lt. Col. R. A. Hay) made a reconnaissance of the Rock, chosen a site and put the necessary work of construction in hand.

[9] An existing tunnelling shelter at Lord Airey’s Battery was to be adopted to provide accommodation for a group of five (later changed to six) men with their wireless installation and all stores and water necessary to maintain them for a year.

[14] He (Commander Birley, S.O.(I) Gibraltar) found excavation in progress but the selected chamber and adjoining compartments many months from completion.

[15]  The cubic capacity of the chamber in which the proposed party would live was to be 57,600 cubic feet; its dimensions 45′ X 16’ X 8’.

[16] It was 1350’ above sea-level.

[17] Ventilation would be provided through two look-out apertures, one looking due E over the Mediterranean and the other W over the Straits and harbour, each measuring 12 inches by 6 inches.

[18] There would be a 10,000 gallon water-tank available.

[19] Priority of construction was being given to the passage-section designed to contain the wireless installation.

Numeric references in relation to the sentence number from ADM 223/464, pp268-270, TRACER. Download a transcript here.

The record states that an existing tunnelling shelter at Lord Airey’s Battery was used for Tracer, so I tried to trace its construction in the war diaries of the tunnelling companies and in the official history of tunnelling from 1939 to 1945 in Gibraltar. The nearest I found was a reference in a document called The Tunnels in Gibraltar, 1939 – 1945, history and development which is held in the National Archives under WO 227/30. Here we find out that in 1941 a tunnel called Lord Airey’s Tunnel was completed. Both the time and location fit with this being Tracer.

Further confirmation of the location is given in line [16] where it tells us the selected tunnel was 1350 feet (411.5 meters) above sea level. There are only a few places on the rock this high, including around Lord Airey’s Battery. The elevation can be read from maps of the area and the survey benchmark at the rear of the gun battery.

The only line in the official record describing the selected tunnel is line 17 where it says “Ventilation would be provided through two look-out apertures, one looking due E over the Mediterranean and the other W over the Straits and harbour, each measuring 12 inches by 6 inches.” Perhaps this was the original idea, but based on the two apertures in the tunnel identified as Tracer, this is not the case. The east aperture may have enabled ventilation, but the small size of the west aperture would not have permitted sufficient airflow.

Based on the wind diagram for Gibraltar the prevailing wind is from the east, known as the Levanter. Being strongest between May and October this wind carries moisture and when it hits the cooler air from the west creates a thick, low cloud that often covers the top of the Rock.

When a Levanter is present, visibility from the Tracer position would have been nil.

The conditions inside many of the tunnels could be unpleasant. One official history of the Second World War tunnelling in Gibraltar10WO 227-30 Report on Tunnelling in Gibraltar stated that there was “natural ventilation in all systems which do not have dead ends” and with a general humidity in the tunnels of 90-95% at times, a dead end tunnel could be very unpleasant indeed. Temperatures are noticed as bring 62°F-65°F (16°C-18°C) throughout the year. Considering siege conditions, where groups would be forced to take refuge in the tunnels, it was also said that “the body heat of occupants (of fully occupied chambers in siege conditions) produces an intolerable condition within a few hours.” The design and construction of the tunnel as we know it would not have been a pleasant place to live, confined, for over a year. In WO 227/30 some notes on the conditions in living huts underground were noted, and they didn’t appear favourable to a Tracer team; “standard hutting without lining, heating or air conditioning, (is) quite unsuitable for the storage of any corrodable materials, and even furniture stored in these huts has grown fungus.” This wasn’t always the case and the author gives examples where sensitive equipment has been stored without issue, but in these cases, electric heating was provided. There is no evidence of heating in Tracer.

Image copyright Imperial War Museum IWM GM63.


Reference is often made to two observation posts in the Tracer tunnel, but in reality, there was only one, a small slit barely 20mm high and cast out of concrete, overlooking the naval dockyard and bay. The slit has been well camouflaged and appears to be barely discernable from the outside (although I didn’t get the opportunity to look for it during my visit).

Left: External view of the viewing slit (Gibraltar Caving Group via Facebook) Right: Composite view of the interior of the viewing slit (Frontline Ulster)

Standard optics would likely have been used to observe shipping by the team, probably a pair of binoculars. As the only method of communication was through wireless telegraphy, the amount of information that could be transmitted at any one time would be limited. The information that may have been useful to the British admiralty may have included the arrival and departure of U-boats, supply convoys, convoys and battle damage assessments of shipping docking in Gibraltar after attack by allied forces.

When the tunnel was rediscovered in the late 1990s there was found to be a concrete wedge lodged in the observation slit. Speculation by the group who discovered it thought this may have created a camera obscure and the image transmitted could have been focused on a screen inside the tunnel. This theory developed due to the presence of a narrow slot in the wedge. The pinhole principle is only valid when the hole is very small (ie; a pinhole) and the material is very thin.

Screenshot taken from a YouTube lecture given by the Gibraltar Museum on Operation Tracer. Accessed October 2023.


The single aim of Operation Tracer was to observe and report on enemy shipping. To achieve this, communications were critical. And thanks to the official record, we know almost exactly what equipment would have been used to ensure reliable communications. It is a fair conclusion to derive that it was Captain Sandwith who reported the following information after consulting with his senior, Colonel Gambier-Parry:

[19] Priority of construction was being given to the passage-section designed to contain the wireless installation.

[22]  A standard Mark 3 transmitter and an H.R.O. Receiver would be supplied from stock.

[24]  Three small 12-volt 120 ampere hour batteries were recommended together with one bicycle-propelled and one hand-propelled generator.

[25]  No results could be guaranteed without the use of an outside aerial.

[26]  A rod aerial 18 ft. long could be thrust out through the aperture when required.

[27]  The frequency to be used would be about 12 megacycles11Today we use Megahertz / MHz by day and 7 megacycles by night.

Numeric references in relation to the sentence number from ADM 223/464, pp268-270, TRACER. Download a transcript here.

The language used in this report suggests these are recommendations and not necessarily what was deployed during Tracer. It is possible that some of the evidence we find in the Tracer tunnel today was based on initial tests and modifications were made before the communication plan was finalised.

It’s important at this stage to try and talk about the antenna. A radio is a paperweight unless it is paired with an appropriately tuned antenna. While a long wire might suffice for receiving signals, a poorly tuned antenna will result in poorly received signals, and an incorrectly tuned transmitter antenna can damage equipment and result in poor transmission. A suggestion for an 18-foot-long rod antenna is given in the communications proposal. The suggestion was that this could be thrust out of one of the apertures when needed, and withdrawn when not in use.

The two types of antenna that could realistically have been used in Tracer could have been a wire or a rod. A wire antenna, such as those issued to SOE agents in occupied countries, would have been suspended between trees to give it length and height. The only option at Tracer would be to drop it out of one of the apertures, in which case it would fall tight to the rock face. The second option, a rod, would have sufficient rigidity to clear the rock face, ensuring the radiated signal did not reflect off the rocks. With the antenna deployed out of the east aperture, this would provide optimal radiation for reception at Flowerdown in Hampshire (more information at the end of this section).

I plotted an indicative propagation map for a typical spring evening, transmitting from Gibraltar, and with the right equipment reception across most of England is possible. Due to the nature of HF propagation in this model North Africa, Spain, Portugal and France are all areas where the signal may not be received. This will change with frequency, atmospheric conditions, day or night, and a host of other factors.

You can try your propagation experiments online at

Antenna length is also specified depending on the wavelength of the signal being transmitted or received; which for 12 megacycles (m/c) is nearly 25m (82 feet) and for 7 m/c is nearly 43 meters (141 feet). Thankfully antennas can work quite well at factors of the wavelength, such as half or quarter wavelengths, etc. The choice of 18 feet is roughly a quarter wavelength for 12 m/c and an eighth for 7 m/c. An antenna 18 feet (5.5m) long that has to be assembled, or at least manoeuvred out one of the apertures daily is not an easy task. Rod antennas are designed to be erected vertically with guy ropes supporting them, mounted to a solid base or ground spike. Thrusting, as the text suggests, this rod out of the tunnel may not only have caused the rod to bend but if done during daylight hours would have likely attracted some attention to the occupant’s activities. However, we can not confirm that a rod antenna was ever deployed.

Below are two images of what may remain of an antenna in the tracer tunnel. Lying alongside the stairway to the west aperture, it appears as if this tube and fitting were once installed inside one of two pipes embedded into the concrete. At one end is a solid threaded fitting, much like a bolt that an antenna feeder cable could be attached to, but the more telling sign is at the other, now broken end. Inside this is what appears to be a form of coaxial cable; the two conductors run parallel with each other, normally separated by a dielectric insulating material. The outer material is known as the shield and the internal cable is the conductor. They are common cable types for carrying signals and are frequently used in radio antenna systems. Based on the corrosion colours it appears as if this cable is made from copper, a highly conductive and flexible material for antenna feeder cables.

The inclusion of Captain Sandwith on the Tracer planning team is an indication that the Naval Intelligence Department, Section 9 (N.I.D.9) were the recipient of the intelligence messages sent from Gibraltar. Section 9 was a Y-service responsible for intercepting enemy naval communications and their headquarters at RAF Flowerdown in Hampshire was expanded in 1942 and a new rhombic antenna system was installed giving high-frequency coverage of the Mediterranean. There was already a Section 9 Y-station located in Gibraltar, but if an invasion happened this would be forced offline and the only on-rock communication would have been the Tracer team.

HMS Flowerdown antenna field in 1942. Encoded transmissions from the Gibraltar Tracer team would have been received and decoded here. Crown Copyright, accessed from a BBC article in March 2024


There is of course the problem with power in the tunnel. Any external source of power from outside the tunnel system would be liable to be cut off should the enemy take over the Rock and the batteries sited just above the Tracer tunnel. It wouldn’t be feasible to utilise a generator inside the cave as this would cause too much noise and smell, but the fuel required to sustain an operation for the 1-year minimum would be prohibitive.

Three small 12-volt 120 ampere hour batteries were recommended together with one bicycle-propelled and one hand-propelled generator.

Statement contained in ADM 223/464, pp268-270, TRACER. Download a transcript here.

The generator itself may have been an issued military item; Battery Charger No. 2. This had an output of 7 volts at 3 amps while turning at 100 rpm. However, doing some rudimentary calculations using the charger above, it would have taken over 72 hours to replenish the 3×120 ampere-hour batteries to only 50%. Power consumption of the radios was low, the HRO drawing between 0.4 and 0.6A when powered at 115v. When the transmitter was operating at a maximum 30W transmission power it would only draw 2.5 amps at 12v, meaning the transmitter could operate for a total of 10 hours, draining the batteries to around 30%. Given that each transmission would have been perhaps a few minutes or so, this would have been sufficient.

It was not just the radios to be powered, if the team were to have any light it’s likely there would have been a few bulbs also powered by the batteries. When you come to discover the debris on the floor of the radio room, you’ll find a light switch, bulb fitting, and some electrical cables. A strong indication there was lighting in this room at least; there are no signs of this anywhere else.

There is one last tantalising clue that may indicate there may have been electricity running to the Tracer tunnel. In the outside tunnel shared with Lord Airey’s shelter, behind the corrugated iron tunnel lining and the concrete poured behind this lining, is a twisted pair of cables. I had not noticed this on my visit and it was only when subsequently examined the photographs that I spotted it. It was likely cut when the caving group were demolishing an entrance into the tunnel. Normal services in the tunnels are typically run externally for ease of maintenance and repair. To bury a cable behind the lining suggests it was not part of the standard services installed into the tunnel.

  • 1
    The British Resistance Archive,, accessed 28 March 2024
  • 2
    Royal Navy
  • 3
    Royal Naval Volunteer Reserve
  • 4
    Royal Marines
  • 5
    Military Intelligence Section 6
  • 6
    Wireless Telegraphy, morse code transmitted over the radio
  • 7 accessed 28 March 2024
  • 8 accessed 28 March 2024
  • 9
    Ruslan Budnik, War History Online, 20 March 2019
  • 10
    WO 227-30 Report on Tunnelling in Gibraltar
  • 11
    Today we use Megahertz / MHz
  • 12
    Screenshot from an early documentary on the discovery of the Tracer tunnel
  • 13
    IWM HU56739 accessed 28 March 2024