Why are unexploded WW2 bombs still found?

As I was walking home last night, an unmarked police car, with the siren on, sped past me. Then, two more followed.

“That’s strange”, I said to my dad who was on the phone. The town I live in, Exmouth, is normally pretty chilled out. “There must be something going on at the Marina”.

It turns out, a WW2 unexploded bomb was found in Exmouth Marina. Curiously at nearly the same time, one was found in Plymouth too.

In Exmouth, initially people 100m around the discovery area were evacuated. Then, the cordon was moved to 400m. It may be moved further.

This is not an official news channel, I’d recommend following BBC or this East Devon Council page.

That said, I thought it would be interesting to look at why we are still finding unexploded WW2 bombs, over 80 years after the war ended.

1. The scale of bombing was huge

During the Second World War, millions of bombs were dropped across Europe. Britain was heavily targeted during the Blitz and later raids, particularly ports, railways, factories, fuel storage sites and coastal infrastructure.

Plymouth was hugely hit due to its position as a naval base. Exmouth was hit much less, but its proximity to Exeter, which was a victim of the Baedecker Blitz, meant that many planes flew over the town, up the Exe to make their way to the city.

But, it seems some were dropped but didn’t explode – when you drop bombs in that quantity, some are guaranteed not to work as intended.

Rough estimates suggest around 10 percent of bombs failed to explode. That still leaves hundreds of thousands buried in towns, fields, rivers and seabeds across the UK.

2. Many bombs were designed to bury themselves

A lot of German bombs were fitted with delayed-action fuses. Instead of exploding on impact, they penetrated deep into soil, sand or mud before detonating later.

The idea was to cause more structural damage and make repairs dangerous. In practice, many of those fuses failed. The bomb went underground and stayed there.

In coastal towns, bombs often ended up in estuaries, harbours and mudflats. Over time, silt covered them completely.

3. Water preserves them better than land

It sounds counterintuitive, but bombs underwater can survive for decades.

Oxygen-poor environments slow corrosion. This means that a device dredged from a marina might be in better condition than one found in a field.

That is why discoveries often happen during dredging, harbour works or flood defence projects. This is what happened in Exmouth Marina.

4. We are digging more

Many finds now happen because of modern activity.

They’re often discovered during construction, housing developments, rail upgrades, utility work and coastal engineering. This disturbs layers of ground that have been untouched since the 1940s.

Taking Exmouth Marina as an example – the deeper the dredge, the higher the chance of hitting wartime debris.

5. They remain dangerous

Even after 80 years, these bombs can still detonate. They have caused injuries and even deaths in Germany, where they are found more frequently – such as this 2021 Munich bomb detonation.

Explosives can become unstable as they age, as fuses corrode unpredictably. That is why police set large cordons and treat finds as major incidents.

A “very large” bomb, like the one reported in Exmouth, often means several hundred kilograms of high explosive.

6. Why this will keep happening

As sea levels rise and coastal towns invest more in flood protection, marina expansion and dredging, discoveries are likely to increase rather than disappear.

It’s likely to carry on happening across the country (and elsewhere in Europe) in 2026 and beyond.