'Castles of the air': Defending the Tower of London during the Second World War
Date: 10 November 2025
Author:
Minette ButlerThe Tower of London moat has protected the fortress for hundreds of years. But when London faced the fury of the Blitz during the Second World War, this very medieval defence found a new way to protect the city from the sky – a huge hydrogen-filled 'barrage balloon'.
Here, Assistant Curator Minette Butler highlights the vital role played by ordinary people in defending the fortress, including the Women’s Auxiliary Air Force (WAAF).
A fortress under fire
The Tower of London during the Second World War
The Tower of London played many roles in the Second World War, from an active barracks to a prison and site of execution. But the Tower was not immune to the destruction wrought by the London Blitz.
Bombs reduced buildings around the fortress to rubble, and five members of its community lost their lives – along with many more on the Wharf, Tower Pier and the nearby river.
Image: A barrage balloon over the Tower of London in around 1939. Heritage Image Partnership Ltd / Alamy Stock Photo
What was a barrage balloon?
Inflated mostly with hydrogen and raised on heavy metal cables, barrage balloons forced enemy aircraft to fly higher. This increased altitude disrupted the aim of attacking planes and made them easier to shoot down during air raids.
Barrage balloons became an icon of the British war effort. Described as ‘castles of the air’, these floating, silver sentinels were strong assets for public morale as visible signs of air defence.
Read more: The Tower of London and the Second World War
The first balloon rises above the Tower
On 8 October 1938, the RAF raised a barrage balloon in the dry moat at the Tower of London. This was part of a city-wide balloon test, organised in response to rising tensions after Nazi Germany invaded Czechoslovakia.
The balloon was tethered to a mobile winch near the Byward and Middle Towers and flown at a test height of around 6,000 feet. Yeoman Warders were invited to inspect the site, and the spectacle drew large crowds.
Image: A barrage balloon flying over the Beauchamp Tower at the Tower of London. ACME / Historic Royal Palaces
If the old grey walls of the Tower could talk, I wonder what they’d have to say?
A reporter marveling at the spectacle of the barrage balloon above the Tower of London
This first balloon at the Tower was removed after just two days. However, the test was a success. On 1 November 1938, the RAF formally established ‘Balloon Command’ which set up balloon groups across the country- a careful precaution that anticipated the war to come.
Image: View from the Beauchamp Tower at the Tower of London, taken in 1945, looking towards the Byward and Middle Towers (now the main entrance for visitors) and the site of the barrage balloon during the Second World War. © Historic Royal Palaces
Protecting London from the sky
The Tower’s balloon crew is mobilised
On 20 September 1940, another barrage balloon returned to the moat to protect the city against the Blitz. Balloon Command had sprung into action on the outbreak in 1939, but the Tower site was mobilised later to thicken London’s defences.
Balloon operation was heavy and dangerous work. The Tower’s crew (mostly paid volunteer airmen from the Auxiliary Air Force) could be out raising, lowering and repairing their balloon at all hours, in all weathers and often right in the middle of air raids.
Fire, breakaway and a hidden landmine
On 30 December 1940, the Tower crew raised their balloon to avoid sparks from a nearby fire – probably still burning from an intense raid the night before. However, things quickly got complicated. During the flight, a cable collided with the side of the fortress, firing the rip link and releasing the gas bag from its tether.
The crew scrambled to retrieve the deflated balloon and reported the breakaway to their squadron. However, barely 8 minutes after their call, the site signalled again. Amidst the activity, someone had discovered an unexploded land mine! The Tower’s garrison ordered an evacuation and, thankfully, everyone escaped unscathed.
The Women’s Auxiliary Air Force (WAAF) Take Over
By 1941, the RAF was anxious to transfer the auxiliary airmen to other roles on the front. Loathe to leave cities undefended, some officials suggested training volunteers from the Women’s Auxiliary Air Force (WAAF) as balloon operators. Many of these women already served as drivers, fabric workers and other vital roles in Balloon Command.
Not everyone supported this plan. Some senior officers felt that the WAAFs couldn’t handle such strenuous work, while others worried that it would reflect poorly on the male operators for apparently doing a ‘woman’s job’.
Nonetheless, early experiments were considered successful, and soon more airwomen volunteered for training. By the end of 1942, around 15,700 WAAFs had replaced over 10,000 male operators on sites across the UK.
Image: On 19 April 1943, Air Marshall Sir Leslie Gossage, head of Balloon Command, and Mrs Sloane Colt, head of the US Red Cross, paid a visit to the Tower crew. © IWM (CH 9441)
The Balloon Operators of the WAAF will still have to endure the weather as well as attack from the air, but they have already shown they can take it. Theirs is undoubtedly one of the hardest jobs undertaken by women in this war, but they have tackled it and succeeded at it.
Ministry of Information in A Roof Over Britain, 1943
'Good and steady'
WAAFs under fire in the Tower moat
We don’t know when the first WAAFs were stationed at the Tower of London. However, by 1943 they’d become one of many all-female balloon crews working across the country. The Tower’s WAAFs even lived in prefabricated huts erected in the moat.
One WAAF stationed at the Tower was Corporal Dorothy Harrison, who served on various sites around the East End, aged just 18. Dorothy described balloon operation as ‘the hardest two years of [her] life’ – battling dangerous weather and even witnessing the death of a fellow airwoman killed by shrapnel on another London site.
The ‘airwomen at the Tower’ attracted interest from the press; fascinated by the WAAF’s unusual balloon site, the Daily Herald proudly stated that ‘they guard the Tower’.
In 1944, Nazi Germany launched Operation Steinbock - the largest series of bombing raids on London since the Blitz.
Faced with renewed enemy action, the Tower’s crew stood firm. In March, a Commanding Officer visited the WAAFs during an air raid and found them ‘good and steady’. Reports from the site indicate that the balloon remained operational throughout the V1 ‘flying bomb’ attacks near the Tower in July 1944.
Image: A barrage balloon being prepared for inflation in the Tower of London moat in 1938. ACME / Historic Royal Palaces
The final chapter
The end of Balloon Command
By August 1944, changing tactics and increased risk to friendly aircraft meant the London barrage was coming to an end. By the end of the year, all balloons in London were deflated and WAAF operators were declared obsolete. Balloon Command finally stood down in February 1945.
However, the Tower’s balloon was not completely forgotten. A circle of concrete tethers, used to control the cables and inflated gas bag, could still be seen in the west moat as late as 1948.
Legacy of the Tower barrage balloon
The Tower of London’s barrage balloon was one of many ways that the fortress ‘did its bit’ during the Second World War.
An iconic symbol of wartime Britain, this curious story reveals how ordinary people defied danger and prejudice to protect the Tower and the city from destruction.
Read more: The Tower of London and the First World War
Selected sources
- No. 30 (Balloon Barrage) Group Operations record book, AIR 25/575, The National Archives, Kew
- Substitution of WAAF for RAF Personnel, AIR 13/32, The National Archives, Kew
- Squadron Number: 907/908 Summary of Events: Y, AIR 27/2233, The National Archives, Kew
- Squadron Number: 908 Summary of Events: Y, AIR 27/2236, The National Archives, Kew
- Air Ministry. 1953. “AIR PUBLICATION 3234 - the Women’s Auxiliary Air Force.” Ministry of Defence Air Historical Branch (RAF).
- Escott, Beryl E. 1989. Women in Air Force Blue: The Story of Women in the Royal Air Force from 1918 to the Present Day. Patrick Stephens Limited.
- Wychwoods Local History Society. 2000. That’s How It Was: Women in the Wychwoods during World War Two. Clouds Hill Printers.
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