Need to know
Plymouth is home to one of the largest Naval bases in Western Europe
11:31, 15 Jan 2026
Millbay cordon(Image: PlymouthLive/William Telford)
Why are there so many bombs found in Plymouth?
- Plymouth was a primary target for the Luftwaffe during WW2 because it houses HMNB Devonport, the largest naval base in Western Europe. The city served as a critical hub for Allied shipping and repairs, making it a constant focus for enemy air raids.
- Between 1940 and 1944, the city suffered 59 bombing raids. In just one week in 1941, German planes dropped over 6,000 high-explosive bombs and 200,000 incendiaries, creating a massive volume of potential unexploded ordnances (UXOs).
- Experts estimate that approximately 10 per cent of German munitions failed to detonate upon impact due to mechanical faults or soft landing surfaces. Given the thousands of bombs dropped, there were likely hundreds of "dud" devices left buried beneath the city's streets.
- During the Blitz, many entry holes were hidden by the rubble of destroyed buildings or quickly filled with water and mud. In residential areas, garden vegetation often grew over these holes before they could be inspected by civil defence teams.
- After the war, Plymouth was rebuilt rapidly to address the housing crisis and restore the city. Many new structures were built directly over uncleared land, effectively sealing unexploded ordnances beneath the foundations of modern homes.
- Most bombs are found today because modern building projects require deeper foundations than those dug in the 1940s and 50s. Construction workers frequently uncover devices, like the one in Keyham in 2024, and the suspected bomb found at a building site in Millbay yesterday, when digging several meters into the natural soil layer.
- The geography of Plymouth, with its mix of soft clay and marshy areas near the docks, often cushioned the fall of bombs. Instead of triggering the impact fuse against a hard surface, the bombs sank into the earth, where they remained preserved and stable for decades.
- Despite the time passed, the explosives inside these shells remain volatile and can be triggered by vibration or exposure to air. This prompts the large-scale evacuations seen recently, as the risk of a "sympathetic detonation" remains a serious public safety concern.
Read more on the Millbay 'bomb' here: Live: Work to remove Millbay 'bomb' continues after delays