34 Miles of Tunnels Were Dug By the British Military Beneath the Rock of Gibraltar

Photo Credit: 1. JORGE GUERRERO / AFP / Getty Images 2. Matt Cardy / Getty Images
Photo Credit: 1. JORGE GUERRERO / AFP / Getty Images 2. Matt Cardy / Getty Images

A British territory north of Spain, Gibraltar is a beloved tourist destination that experiences naval dockyard actively by the British Royal Navy. Lesser known are the vast networks of tunnels beneath the area, spanning approximately 34 miles, with some dating back to the 1700s.

King’s, Queen’s and Prince’s Lines

Two cannons pointed out of holes in the wall of the Rock of Gibraltar
Tunnel running within the Rock of Gibraltar. (Photo Credit: Bettmann / Getty Images)

While caves within the Rock of Gibraltar may have been used by Neanderthals, the first intentionally-dug tunnels came into existence shortly after its capture by the British in 1704, primarily for use as military fortifications.

Known as the King’s, Queen’s and Prince’s Lines, they took much of the century to finish, as the British were defending against Spanish and French assaults during the Thirteenth (1727) and Great Siege of Gibraltar (1779-83).

Over a thousand meters of interconnected tunnels

Entrance to the Prince's Gallery on the Rock of Gibraltar
Entrance to the Prince’s Gallery on the Rock of Gibraltar. (Photo Credit: Prioryman / Wikimedia Commons CC BY-SA 3.0)

Throughout the sieges, the British carved out the initial true tunnels and “galleries” within the Rock of Gibraltar. Resembling artificial cave systems, they were used to position artillery. By the late 1700s, approximately 1,200 meters of interconnected tunnels had been excavated, linking the various defensive lines that had been established earlier.

These spans encompassed several notable structures, such as the Windsor, Queen’s Union, Upper Union, Lower Union, Prince’s, King’s and Queen’s Galleries.

Gibraltar’s significance as a naval base continued to grow

Cannon pointed out of a hole in the wall of the Rock of Gibraltar, at the end of the Windsor Galleries
Windsor Galleries in the Rock of Gibraltar. (Photo Credit: myLoupe / Universal Images Group / Getty Images)

By the late 1800s, Gibraltar’s significance as a naval base grew, leading the British to expand their underground infrastructure. New tunnels were dug to facilitate access to quarries and for ammunition storage. A notable addition during this period was the Dockyard – also known as the Admiralty Tunnel – which became one of the most significant developments.

Admiralty Tunnel

View down the length of the Admiralty Tunnel
Admiralty Tunnel beneath the Rock of Gibraltar. (Photo Credit: Scott Wylie / Wikimedia Commons CC BY 2.5)

The Dockyard spanned the entire expanse of the Rock of Gibraltar, facilitating seamless access between the active dockyards and the quarries supplying stone. Moreover, between 1898-1915, five underground reservoirs were constructed, to mitigate concerns regarding water supply instability.

Instability in Europe prompts increased construction on Gibraltar

Dimly-lit tunnel beneath the Rock of Gibraltar
Tunnel running beneath the Rock of Gibraltar. (Photo Credit: JORGE GUERRERO / AFP / Getty Images)

Starting in 1936, during the Spanish Civil War and with the rise of the National Socialist German Workers’ Party, the British built hospitals and air raid shelters within the Rock of Gibraltar.

Civilians were also evacuated, turning the territory into a military stronghold.

Outbreak of World War II

Royal Engineers digging a tunnel beneath the Rock of Gibraltar
Royal Engineers digging a tunnel beneath the Rock of Gibraltar, 1941. (Photo Credit: Lt. G.W. Dallison, War Office Official Photographer / Imperial War Museums / Wikimedia Commons / Public Domain)

With the outbreak of World War II, more tunnels were excavated, with the intention of serving as military barracks and storing equipment. The British and their allies stationed at Gibraltar constructed an underground city with facilities ranging from a power station to a bakery. These enhancements enabled Allied troops to be accommodated underground for up to 16 months, if necessary.

‘Stay Behind Cave’ and Operation Tracer

View down the length of one of the tunnels beneath the Rock of Gibraltar
One of the tunnels beneath the Rock of Gibraltar. (Photo Credit: Wolfgang Kaehler / LightRocket / Getty Images)

One of the most unique tunnels from this era remained concealed for over 50 years. Known as the “Stay Behind Cave,” it was dug as part of the covert Operation Tracer and was intended as a refuge for British spies, in case Gibraltar was captured by the enemy.

Between 1936-39, two miles of tunnels were constructed, and from 1939 until the conflict’s conclusion, 18 additional miles were added, expanding the total network to 25 miles.

Tunnel expansion continued following World War II

Dimly-lit interior of a Nissen hut
Nissen hut within the Rock of Gibraltar. (Photo Credit: AquilaGib / Wikimedia Commons CC BY-SA 3.0)

Following the conclusion of the Second World War, the expansion of the tunnel systems in Gibraltar continued, albeit at a reduced pace compared to earlier years.

During this period, several tunnels were primarily used for storage purposes or as reservoirs. The final one beneath the Rock of Gibraltar was completed in 1967, and the last group of specialized tunnel workers was disbanded the following year. By then, the tunnels stretched over 34 miles in total length.

Rock of Gibraltar, today

View down a stretch of tunnel beneath the Rock of Gibraltar
Tunnel running beneath the Rock of Gibraltar. (Photo Credit: Matt Cardy / Getty Images)

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Today, there’s little necessity for military fortifications on Gibraltar, as the presence of the British Royal Navy has significantly decreased. However, the tunnels haven’t been entirely abandoned; many of them are now accessible for visitors to explore. Among the most popular are those dating back to the Great Siege and a select few from the Second World War that are open to the public.

Rosemary Giles

Rosemary Giles is a history content writer with Hive Media. She received both her bachelor of arts degree in history, and her master of arts degree in history from Western University. Her research focused on military, environmental, and Canadian history with a specific focus on the Second World War. As a student, she worked in a variety of research positions, including as an archivist. She also worked as a teaching assistant in the History Department.

Since completing her degrees, she has decided to take a step back from academia to focus her career on writing and sharing history in a more accessible way. With a passion for historical learning and historical education, her writing interests include social history, and war history, especially researching obscure facts about the Second World War. In her spare time, Rosemary enjoys spending time with her partner, her cats, and her horse, or sitting down to read a good book.

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