Unexploded WW2 bombs: Who finds them and how common are they?

All the gen on Britain's unexploded bombs from the Second World War

It feels normal to switch on the news and see reports of an unexploded bomb find. Yet, the consequences of such a discovery can be severe to communities around the location of a found device. Evacuations, road closures, business shutting down, and of course, risks of structural damage to properties and even death are all realistic outcomes when a rusty bomb is unearthed.

Unexploded ordnance (UXO) discoveries are almost always related to the Second World War, which concluded more than 75 years ago. However, the consistency of bomb finds shows no signs of letting up – quite the contrary.

Here is an examination of what happens when a bomb is found and some notable examples of significant discoveries over the last 75 years, and what a UXO expert suggests about how likely bomb finds are and how businesses mitigate against them.

A larger bomb detected and disposed of by Zetica UXO. Credit: Zetica UXO

What Is An Unexploded Bomb?

This might seem like a silly question, but there are various types of explosive devices that, when found, require professional and sometimes emergency responses.

The most common finds tend to be 500lb German bombs in key locations around the UK - the targets of Hitler's Luftwaffe during the war. But alongside these High Explosive (HE) bombs, there are also discoveries of parachute mines and incendiary bombs – of which up to 50% may not have detonated upon impact.

There can also be, on rarer occasions, discoveries of much larger bombs, like that found in Exeter earlier this year.

In March, a 2,200lb unexploded WW2 bomb led to a widespread evacuation and structural damage to properties once the controlled explosion of the device was conducted by military bomb disposal teams.

The crater left by the explosion was deep enough to hold three double-decker busses.

According to experts, there are also discoveries of other types of ordnances, such as grenades, shells or ammunition, which are becoming more frequent. But why is that?

The unexploded WW2 bomb found in Exeter was a 2,200lb explosive device. Credit: Devon and Cornwall Police

Are Unexploded Bomb Finds Becoming More Common?

It seems to be the case that more unexploded bombs are being discovered, and for good reasons.

Firstly, building developments in inner-city areas have increased over the last decade. When a site is developed, it is ethical for the businesses behind the projects to have the land surveyed by professionals who can help detect unexploded bombs and assist in their disposal. It is important to say here that although the MOD can respond to discoveries of bombs, it does not provide detection services or surveying of land. As such, specialist companies are contracted by developers to conduct that work.

One such company, Zetica UXO, said that when workers at construction sites discover an unexploded WW2 bomb, it is not always possible for the military to provide support. That is where companies like Zetica UXO can step in and provide consultancy and disposal.

Mike Sainsbury, MD of Zetica UXO, said:

"10 years ago, only the military could deal with finds of unexploded bombs. Nowadays, it isn't always possible for the military to support with construction finds. 

"If you have a commercial project going ahead, and risk exists, mitigation can be put in place to limit that risk.

"I have the utmost respect for the military, but they aren't going to come out until you find something. Whereas, if there is proper planning and time, we can come in and limit risks.

"It is not just about disposal. Commercially, we can come in and do geophysical surveys. We can prepare fully and even build large bunkers if needed. 

"So, although it will cost, the final disposal is less disruptive."

How Many Unexploded Bombs Are There?

It is not possible to say how many more unexploded bombs may be found in places like London, Coventry, or Exeter. However, during World War Two, a Bomb Census was undertaken each time an attack occurred, so it is possible to understand the more likely places devices may lie.

Exeter was targeted as part of Hitler's Baedeker Raids in April and May 1942 – named after tourism guidebooks used by German planners to devise their target lists.

The city was targeted to damage the British population's morale instead of for strategic purposes to do with war capabilities.

During the Blitz on Exeter, 7,000 bombs were dropped throughout 19 attacks. It resulted in the loss of 300 lives.

During the Second World War, in London alone, 12,000 metric tons of bombs were dropped. It resulted in the deaths of 30,000 civilians.

Up to 10 percent of High Explosive, or HE, bombs are estimated to have failed to detonate. For incendiary bombs, the figure could be as high as 50 percent. That means many bombs likely remain unfound in cities around Britain.

Zetica UXO told BFBS that smaller bombs, typically dropped by German bombers during the Blitz are not necessarily easier to deal with than bigger explosive devices, as a lot depends on their location. Credit: Zetica UXO.

What Should You Do If You Find An Unexploded Bomb?

Zetica UXO's Mike Sainsbury explained that it is not just construction site workers or land surveyors finding explosive devices. He said:

"We monitor a lot of newsfeeds around the subject of bomb finds and have observed a big increase in magnet fishermen finding explosives at the bottom of canals. 

"It's averaging one per week."

Magnet fishing is an outdoor activity in which enthusiasts search bodies of water for objects hidden from sight. According to Mr Sainsbury, coronavirus lockdowns have led to more people taking up the hobby, which has increased the number of dangerous items found in canals and lakes.

Mr Sainsbury added:

"It is getting to the stage where I believe there needs to be some formal regulation around magnet fishing.

"People are commonly finding unexploded grenades that have somehow come to rest on canal beds. They may have been dropped there by Home Guard members during the war.

"There is a moral imperative to report finds like this to the police."

The unexploded WW2 bomb found in Exeter in March 2021 cause substantial damage to nearby properties. Credit: Devon and Cornwall Police.

What Does It Cost To Have A Bomb Disposed Of Safely?

If an unexploded World War Two bomb is discovered by a member of the public, the emergency services should be called immediately. Like the device found in Exeter, Military EOD units can be deployed to safely detonate the bomb with little consequence to life and property.

However, in the Exeter bomb find of March 2021, the device was so large that substantial damage to surrounding properties did occur during the making safe process. Thankfully, this is rare.

Mr Sainsbury said that an outcome like that seen in Exeter is precisely the sort of thing building developers want to avoid. That is where his company can step in and help.

But what does it cost?

He said that the cost of coming in and dealing with an unexploded bomb can vary, adding:

"It could be anything from a few thousand pounds right up to £100,000. 

"One of the key questions effecting costs is the location of the device. We might have to build blast protection for example, and soon the costs can build."

In 2017, a Freedom of Information Request to the Ministry of Defence asked what the costs were of attending a callout to an unexploded WW2 bomb. In response, the MOD said that it did not hold information on specific costs, but that matters including the size of munition, its location in the UK and where the item is situated are all variables to overall costs. It added:

"You may also find it helpful to note that costs are not routinely captured on an incident by incident basis for the disposal of World War Two munitions." 

A larger and more complex device attended to by Zetica UXO at an ex-military base in England. Mitigations like this take longer to plan and execute, the firm told BFBS. Credit: Zetica UXO

Dad's Army Bomb Losses

In 2017, road workers in Plymouth found a cache of 10 self-igniting phosphorous grenades, resulting in road closures and emergency response by bomb disposal experts.

Unconfirmed reports suggested the grenade stash could have resulted from Dad's Army-type Home Guard efforts to hide munitions to be used later should the country be invaded by Nazis.

At the time, the Plymouth Herald reported that "dozy members of the Home Guard" may have been responsible for losing the grenades. A military historian, Ryan Corder, told the newspaper:

"They were sometimes hidden away to be recovered and used in case of German invasion, except some units forgot where they were.

"I have one of the original wooden crates."

Bombs dropped by Germans during the war were fitted with electrical fuses, which, thankfully, depended on battery power. 80 years on from when they were installed, the fuses are now likely dead. However, the explosives remain and could be ignited due to changes in their surrounding environment, including direct impact, vibration, or heating.

Therefore, vast quantities of unexploded devices could sit in the mud beneath new property developments, or idly at the bottom of the Thames, and there is a possibility of them being disturbed, one day, which is why the Ministry of Defence's EOD teams will continue to be ready.

For companies like Zetica UXO, their expertise in locating devices before they even become a problem to communities is crucially vital.

The population might sleep better at night knowing there are people out there still looking for bombs left over from the terrible days of World War Two.