Why Sheffield remains 'high risk' for unexploded WWII bombs - and where they’re most likely to be

Buildings had been razed, more than 650 people were dead and a tenth of the population found themselves homeless in the worst Luftwaffe attacks the city would see for the duration of the Second World War.

As Sheffield rebuilt itself over the years, those who witnessed the devastation of the December air raids of 1940 might have hoped they’d seen the back of German bombs for good.

What they might not have anticipated was these bombs turning up decades later, stumbled upon by unsuspecting civilians like the one who tripped over a mortar shell tail in the Peak District just this week.

With up to one in ten German bombs dropped over the UK during the war failing to explode, it’s almost certain that dozens more lie hidden under the streets of Sheffield today, yet to be discovered and safely removed.

It’s a probability so strong that consultants Fairhurst designated Sheffield a “high risk” city for unexploded devices as recently as 2017.

Sheffield bomb locations

Sheffield was a target for German bombers as it was home to the Vickers factory, the only site in the UK capable of producing Rolls-Royce Merlin crankshafts for the Spitfire and Hurricane aircraft, along with components for tanks, deck armour for warships and bomb castings.

During the two air raids of 1940, around 355 tonnes of high explosives and 16,000 incendiary canisters were dropped across the city, including residential areas as well as industrial quarters.

Due to the sheer volume of bombs dropped, it’s been extremely difficult for experts to determine the exact number and location of those that failed to explode. Historians believe faulty mechanisms as well as sabotage may be to blame for the duds.

The areas most heavily targeted by the Luftwaffe, however, are those most likely to be harbouring unexploded bombs.

The Moor was completely devastated by the attack, for instance, while every building in Angel Street was damaged by fire or burned. King Street suffered huge damages, and Sharrow, Broomhill, Neepsend and Burngreave were also subject to attack.

Recent discoveries

A map produced by Unexploded Ordnance specialists Zetica backs up this theory in places, showing, for example, three unexploded bomb discoveries in and around Burngreave since the war.

Bombs have been also discovered in Hillsborough, Don Valley and Owlerton Stadium, as well as in more central city locations like Matilda Street, where four bombs were successively discovered in 2016.

Though locals do occasionally stumble upon unexploded bombs, more often it’s builders who discover the dud explosives when digging into the ground to establish building foundations.

In the majority of cases, bomb squads are called in to deal with the problem, and everyone gets out unscathed.

An estimated 15,000 military items were extracted from UK construction sites between 2006 and 2008, according to the Construction Industry Research and Information Association (CIRIA) which released a guide on safety around unexploded bombs in 2009.

Is there a risk to public safety?

The story isn’t the same every time, however, and one of the biggest dangers of unexploded bombs is their unpredictability.

Bomb disposal units often have very little information about how long the bomb’s been there and how it might have changed over time.

In 2014, a German digger driver was killed after accidentally striking an unexploded British device while working in the North Rhine-Westphalia region.

In the UK, past discoveries have led to mass evacuations in Bath, London, Birmingham, Portsmouth and Essex.

As buildings get taller, foundations have to go deeper - meaning it’s likely Sheffield will see yet more unexploded bombs surface over the next few years.

Though they pose little risk to the everyday life of locals, these remnants of World War Two are a stark reminder of the horrors Sheffield suffered not so long ago.