The Hay’s Level tunnel complex forms part of a vast tunnel system initially built by the Royal Engineers during WWII to provide stores, accommodation, hospitals and underground electrical generators providing support for British troops defending the Rock from a possible German invasion under the codename Operation Felix. The tunnel system was later expanded to accommodate up to 30,000 troops who would later take part in Operation Torch, the Allied invasion of North Africa in 1942. 

The Hay’s Level section comprises a Royal Mechanical and Electrical Engineer workshop and a Royal Army Ordnance Corps offloading depot. A further section of the tunnel connects with Liddel’s Union. It was named after the Commander of the Royal Engineers, Lt. Colonel Robert Alistair Hay who served as C.R.E., Fortress Engineers in Gibraltar from 1940 to 1944.

Before September 1940, the initial preparatory defence works and tunnelling had been carried out by two small R.E. Coys., together with a single Tunnelling Coy., all under the C.R.E., Gibraltar, with the valuable help of the City Engineer's civilian branch which had been responsible for excavating a series of air raid shelters in 1939. The civilian branch had already been active in the area having built the Willis’s Road Waterworks and excavated the Calpe Road shelter, which would later be amplified and converted into one of five underground hospitals once the civilian population had been evacuated. One of the unfinished reservoirs at Willis’s Road waterworks was temporarily converted into a three-storey barracks and storehouse for the 4^th Battalion the Black Watch tasked with defending the North face and eastside of the Rock.

City Council's staff engaged in construction of a new ward of the hospital.

Calpe ARP Shelter near Willis's Road.

Military tunnelling, however, only began in earnest after September 1940 when Colonel C. E. Fordham the Chief Engineer was appointed, the first such senior appointment since 1925. Fordham arrived from the U.K. together with two C.R.E.s - Lt. Col. D. M. Thompson and Lt. Col. R. A. Hays - two full Tunnelling Coys., (178 and 180), a General Construction Coy., and a Pioneer Coy., which at full strength, comprised some 900 men in all. These were to be followed in early 1941 by an additional Army Troop Coy., and another Tunnelling Coy., (170) making three Tunnelling Coys, in all.

These specialised Tunnelling Coys., were recruited almost entirely from men who had previously worked in the coalmines, i.e., men with no experience of hard rock mining. Still, the officers, drawn from the ranks of the Institution of Mining and Metallurgy proved quite experienced and proficient in a surprisingly short time, the companies settled down to the unusual working conditions and soon began to make noticeable progress. The equipment provided for the tunnelling companies, however, was quite basic - jackhammer drills and small compressors, the latter more suitable for outdoor field work than the continuous service of rock drilling around the clock.

The rate of excavations increased considerably in 1941 when the 1^st and 2^nd Tunnelling Companies Royal Canadian Engineers, some 300 strong were deployed to Gibraltar. The Canadians were fully equipped with modern diamond drillers that drilled wet with drifters enabling them to do invaluable prospecting work that was beyond the capabilities of the British tunnelling companies.

From the time the first tunnels had been built during the Great Siege right up to 1939, around 7 miles (11.26 Km) worth of tunnels had been excavated. Between 1941 and 1943 it is estimated that a further 18 miles (29 Km) of tunnels were built amounting to around 935 million cubic feet of rock were excavated by the combined efforts of these four Tunnelling Companies. Most of the rock and debris from these works was put to good use enlarging the airfield runway. By the early 1960’s, when most of the tunnelling works had been completed around 34 miles (54.7 Km) of tunnels had been completed, more than twice the length of roads in Gibraltar at that time.

3rd Tunnelling Engineers Company deployments to and from Gibraltar.

Private John Gunn 180 Tunnelling Coy. R.E. working inside the Gibraltar Tunnels. (Courtesy Hugh Toal).

Tunnelling works were divided into three phases. Phase I covered the initial urgent requirements of the Fortress, consisting primarily of accommodation for the garrison of the North Face with a tunnelled hospital and safe storage of supplies as a second priority. Each company consisted of 120 men working in eight-hour shifts twenty-four hours a day. All spoil removal was necessarily manual and all ‘mucking’ operations was carried out by men from other units, and given the nickname ‘The Muckers’. Working parties were nevertheless difficult to arrange, as there was so much other work to be done preparing defensive positions throughout Gibraltar in anticipation of Operation Felix. This first phase covered approximately the period from June 1940, to January 1942.

Phase II covered by far the largest yardage of excavation works.  Planning and survey were now well ahead of actual tunnelling, the work consisted of straightforward galleries and chambers in proved good rock and the plant situation had much improved. After this phase, around March 1944, all essential work to enable the garrison to withstand a year's siege was virtually complete and the Tunnelling Coys., began to be withdrawn in preparation for the Normandy Landings, which followed a few months later.

During Phase III, only one Tunnelling Coy., remained on the Rock. Having inherited all the resources accumulated during the war, this company worked under ideal conditions until its withdrawal and the cessation of all tunnelling work at the end of the war.

Programme of tasks for the Tunnelling Company Royal Engineers and City Council on Gibraltar to complete from 1 October 1943 onwards.

2nd Tunnelling Company Royal Canadian Engineers at Grand Parade circa 1941.

Hay’s Level was built during Phase I of the tunnelling project by members of 178 Tunnelling Coy. Excavation of Hay’s Level began at Willis’s Elbow where a reinforced concrete wall was erected to screen the tunnel entrance. Within this thick wall, a machine-gun bunker covered the Willis’s Road as it approached the bend.

Within the tunnel entrance, a blast trap and concrete plug (now removed) protected the tunnel interior from any potential blast or shock wave exploding near the entrance. The conventional blast walls were considered impractical for vehicular traffic so the blast trap method was adopted on the recommendation of the Ministry of Home Security. Experiments had shown that the sharper the corners the better, but these had to be angled-off in the case of lorry-sized tunnels such as Hay’s Level. The operation was completed when a concrete plug was inserted into the original straight tunnel. Traps of this type were designed and constructed to permit the passage of three-ton vehicles with little or no inconvenience.

Several smaller recesses and another escape tunnel are located on the south side near the Hay’s Level entrance. These have now been converted into toilets and stores for the WWII Tunnels.

The main section was built wide enough for vehicles to be able to access the two main chambers within Hay’s level consisting of the R.E.M.E mechanical workshop and an R.A.O.C off-loading bay.  The workshop contained several vehicle inspection pits that have since been filled in. Offices and a spare parts store were also located within this chamber. At the far end, a small escape tunnel connected to another smaller chamber containing four large stores. This chamber was also accessible via the offloading bay, but only accessible on foot.

Blast Traps contruction for tunnel entrances. Hay's Level was constructed according to this concept design.

Royal Engineer tunnellers using a water pressure drill to clear solid rock 1st November 1941.

The early stages of construction of the Royal Electrical and Mechanical Engineers workshops at Hay's Level during World War II. This chamber has a span of 16m and a height to crown of arch of 10m and a length of 120m.

The REME Chambers at Hay's Level being cleared of all rubbish and debris.

Hay's Level Loading Bay next to REME Chambers.

Hay’s level connects to the rest of the tunnel network via Liddell’s Union, named after General Sir Clive Gerard Liddell who was Governor of Gibraltar from 1939 to 1941. From here a gallery at a slope of about 1 in 20 leading from the old system in the North Face southwards to the western end of the lower water works tunnel. This included additional and better accommodation for the garrison, some supply and ammunition storage and engine rooms for the lighting and cooking in the whole of the Northern system. The gallery provided covered communications to the back of the town and, via the water works tunnel, to the east side above Catalan Bay.

British soldier at Liddell's Union 1940.

Nissan Huts at Fordham's Accomodation.

By January 1942, most of the excavation for the first programme had been completed, though construction lagged far behind. Concrete floors were laid throughout. Galleries were driven to a slight fall and gutters were provided on one side to carry off all water seepage in galleries and chambers. To speed up construction work Iris and Romney 35 ft. and Nissen 24 ft. and 16 ft. span hutting was ordered from the U.K. and future chambering was excavated to accommodate these huts with just one or two feet spare. This space was essential so that water seeping through the rock could drain away through the drainage channels provided; it also permitted air circulation around the buildings and facilitated periodic inspection of the rock face. Every chamber having a span of more than 12 feet (3.7 m) was arched, the rise being one-fifth of the span. In the early days. spans up to 35 feet (11 m) had been cut with flat roofs, but these gave endless trouble from rock falls, particularly when further excavations were being carried out in the vicinity.

Chambers were also cut parallel to the main tunnel. Normally a pillar of rock 20 feet (6m) to 30 feet (9m) wide was allowed between each chamber and, where one system was being developed above another, a clear rock space of 100 feet (30 m) between the two systems was considered the minimum safe thickness. Small communication tunnels, however, up to 12 feet (4 m) span, were crossed with only 18 feet (5.5m) between the roof of the lower tunnel and the floor of the higher.

Following this pattern, new parallel accommodation chambers were excavated immediately to the south of Liddell’s Union. These chambers were named Fordham’s Accommodation after Col. Henry Marshall Fordham OBE, MC, who was Chief Engineer in Gibraltar. Around 6,000 men would eventually be accommodated within these chambers.

Sheets used for the accommodation huts were given a priming coat of red oxide and two coats of lead base or bitumastic paint before erection (when paint ran out coal tar from the local gas works was used instead). The inside was given a coat of lime wash after completion. Besides being very quick to erect and making the accommodations waterproof, this method gave a more stable roof, which allowed chambering to be done in more inferior rock. Chambers could therefore be spaced closer together.

One downside to this sheeting method was that once erected, the sheeting could not be properly treated again so its life was limited. In view of the great advantage of this system, however, and the fact that the sheeting would probably survive until the end of the war, despite the warm damp conditions promoting rust, this disadvantage was accepted.

Type of Huts used inside the Gibraltar tunnels.

Much of the rock and debris excavated from the tunnels were transported down to the North Front and put to good use surfacing and extending the airfield. By April 1942, the runway had been extended to 1,150 yards (3,450 feet; 1,050 metres), by November 1942 to 1,550 yards (4,650 feet; 1,420 metres), and by July 1943 to 1,800 yards (5,400 feet; 1,600 metres). This last major extension of the runway allowed larger aircraft to land at Gibraltar. These larger aircraft would later be used to transport men and materials in support of the Allied invasion of North Africa, codenamed Operation Torch.

A bulldozer and steamroller being used during the construction of a new aerodrome on Gibraltar, November 1941.

A Douglas Dakota silhoutted against the Rock (IWM).

From Fordham’s Accommodation another large chamber was excavated which also connected directly to the R.A.O.C loading bay at Hay’s Level. This chamber served as both an Assembly Hall and Dining Hall for the troops.

Another tunnel, Willis’s Winze, housed the cookhouse, ablutions and a very large natural water reservoir. A winze is an engineering term for a tunnel built from the top down, whilst a raise refers to a tunnel that has been excavated from the bottom up. Willis’s Winze exits to a large fortified concrete bunker on Willis’s Road.

Tunnels and chambers were planned to take all possible advantage of natural ventilation and this is evident from a cool breeze along Liddell’s Union emanating from tunnel exits such as Amelia’s Incline and Jock’s Balcony. This natural ventilation together with the inclined construction of Liddell’s Union allowed for the construction of large chambers fitted with Romney Huts for dry storage.

On the other side of the passageway, drying rooms and ablutions were constructed.  Water for the ablutions was drawn from a tank built at the end of Amelia’s Incline shaft. A water filtration plant purified the water into two large water tanks, which utilizing gravity could then supply the troops with an abundance of potable water for their everyday use. Another side chamber housed a cookhouse with further storage areas opposite. These large chambers were probably used as an accommodation area for the troops originally being converted into storage areas at a later stage.

A medical officer examining a 'patient' during a training exercise in an underground hospital in Gibraltar, cut into solid rock and which previously served as an air raid shelter, October 1941. (IWM)

'Patients' rest on bunks during a training exercise in an underground hospital in Gibraltar, cut into solid rock and which previously served as an air raid shelter, October 1941. (IWM)

Staff officers conducting operations from the underground defences on the Rock of Gibraltar, 9 April 1942. (IWM)

Men of the Black Watch Regiment observing the scene below using a telescope from a vantage point on the Rock, 4 January 1942. (IWM)

Right at the very end of the Liddell’s Union stands Clapham Junction, so named because from here the tunnel system branches off to other locations. This section also joined the old tunnel section started during the Great Siege with the new WWII works. From here, it is possible to access the Upper and Middle tunnels and connect directly to the Northern Defences. Another tunnel leads down via Thompson’s Switch, to a warren of defensive and searchlight positions covering the Neutral Ground from hidden embrasures on the North Face of the Rock. Thompson’s Raise connects to Farrington and McPherson’s Chambers continuing all the way down to MacFarlane’s gallery and William’s Way situated just above Catalan Bay village.

To the North of Clapham Junction are two exits points leading to a ledge on the North Face overlooking the Isthmus and known as Jock’s Balcony, after the 4^th Battalion of the Black Watch who used this concealed ledge as an observation post during WWII. The Black Watch were garrisoned in Gibraltar from July 1940 to April 1943. Access to the ledge is by a series of blast walls on both sides of the exit points.

Tunnel exit to Jock's balcony. The blast walls protecting the tunnel can be seen on the left of the image.

View from the ledge at Jock's Balcony.

Leading West from Clapham Junction is another tunnel that exits to the Princess Anne and Princess Amelia’s Batteries. A small generating station with two generators provided electricity for the entire underground complex from a small chamber near the exit.

After WWII Hay’s Level and Liddell’s Union continued to be used by the Royal Engineers as workshop and storage facilities until the early 1970’s when all R.E.M.E. facilities were moved to the Arow street and sandy Caves. The entire complex was then handed over to the Gibraltar Government.

In 1978, the old Assembly Hall at Hay’s Level was converted into a touristic facility and disco known as the ‘Laser experience’. In the 1990’s the entire site was opened up as the WWII tunnels. 

1st Fortress Engineer Coy, Gibraltar at the Heathfield Steps, Alameda Gardens, 1945.

Bibliography

Capurro, Ralph: Royal Engineer’s Album Vol 4 at Gibraltar National Archives including articles on the following:

Haycraft, Col. T. W.R: The Gibraltar Tunnels in The Royal Engineers Journal, p. 310-320

Rose. Edward P.F: Tunnelling Companies Royal Engineers in World War II: excavation of bomb-proof facilities in France, Gibraltar, Malta and the UK (2018).

After the Battle No. 21 (1978) Extracts from articles: Construction of the Airfield, The Tunnels, Operation 'Felix'.

Stacey, Charles Perry: Work of Canadian tunnelling units at Gibraltar, 1940-1942. Catalogue number: D63-4-80-1942E-PDF