On a misty Monday morning in June 2008, eagle-eyed construction workers at an Olympic site in Bromley-by-Bow spotted something unusual in their excavations. It wasn’t long before it was identified – it was a very large German bomb.

Very quickly, an exclusion zone was established around the site and workers and bystanders moved to a safe distance. On the railways, services into Fenchurch Street were also suspended. Army bomb disposal experts were summoned from Colchester and work began to make the 1000kg High Explosive device safe – work made more difficult as the bomb sat directly on top of a gas main. In the end, it took almost a week to make the bomb completely safe. Luckily no lives were lost, but the disruption to lyocals, travellers and the workers was extensive.

The discovery of the device was a stark reminder of some of the darkest days in London’s history.

St Paul’s During The Blitz

During the course of World War Two, almost 1.5m incendiary devices and somewhere in the region of 50,000 High Explosive (HE) bombs were dropped on the Capital. Of these, it is generally accepted (based on a Home Office statistical analysis in 1942) that approximately 10% failed to detonate for some reason or other. Those that still remain a problem today are largely of the HE variety.

German Pilots Pose With Their Bombs

Many of these bombs were identified and made safe at the time. Many others detonated shortly after they landed, at a sometimes tragic cost to those trying to defuse them. In the often chaotic and confusing atmosphere of a bomb site, however, some were left behind.

In most cases this was by accident – in the rubble and destruction caused by one bomb it was all too easy to miss another which had failed to explode. Similarly, if a bomb fell in the Thames or another water source it was not always spotted, and even if it was then defusing it was not really practical if it didn’t detonate (most did – one infamously causing a great deal of damage to the Northern Line’s Charing Cross loop, which luckily had already been decommissioned and sealed off from the rest of the network).

Sometimes, the need to get things moving again or the location of the failed device in question simply meant that leaving it in situ was safer than trying to defuse or move it – better to simply note the location and cover it up. Known as “abandoned bombs” many of these still lurk beneath the Capital today. In 1996, for example, the MoD revealed – in response to a parliamentary question by Simon Hughes – that abandoned bombs were still known to exist in Norwood, Ladywell and Deptford Council cemetaries, as well as a wide range of other places both north and south of the river (if you’re the type of person that worries about this kind of thing then you might want to avoid renting or buying on Hazel Grove in Staines).

Breaking the Myth

It’s important to point out here that all of these unexploded devices – be they known or unknown – are harmless whilst they remain undisturbed, as are the many unexploded anti-aircraft shells that likely lurk beneath the Capital somewhere as well. Unexploded Ordnance (UXO to its friends) is unexploded for a reason. HE needs an external catalyst to trigger it, an impetus normally provided by a detonator, and – to put it bluntly – the Germans were very good at making detonators. The detonators on German bombs were generally electric or clockwork, which made them more reliable, but also meant that if they did fail their complexity makes them unlikely to simply start functioning again. The Television and Cinematic image of the uncovered bomb that suddenly resumes ticking is thus essentially a myth – although it is worth pausing to spare a thought for Germany here. The Allies dropped twenty times more bombs on Germany than were dropped on the UK and Allied detonators were far simpler, more temperamental and prone to failure – the tragic result being that whilst no deaths due to uncovered ordnance have occurred in the UK since the War, a number have on mainland Europe.

Aggressive disturbance of UXO can, however, on rare occasions replicate the action of a detonator. A major impact from a piling machine or even an excavator (something which tragically cost the life of a German plant operator during some Autobahn repairs in 2006) could be enough to set an unexploded bomb off, if the HE inside hadn’t degraded. Violent vibration might also be enough should a chemical detonator somehow have retained enough integrity and leaked some of its contents into the soil.

All the above means that, generally speaking, the presence of many elements of UXO beneath the soil of London has little effect on, and poses little risk to, daily life in London. There is one area, though, where it potentially poses a greater risk – large-scale construction.

The Need for Careful Digging

Major construction projects often involve a good deal of demolition and digging, both of which can cause UXO to be uncovered and which could – in a truly unlucky situation – cause it to be detonated. As a result, there are few large-scale construction projects in the Capital today that don’t have one eye on the ground. The possible presence of UXO has meant that most large London projects have had to carry out some level of ground investigation, or factor that possibility into their plans, since the end of the War.

Nowhere is this more true than on the Capital’s transport projects. The design of the Hungerford Jubilee Footbridge had to be amended after London Underground – who have an understandable fear of UXO – objected to the plan to drop pilings in the Thames. The pilings, LU pointed out, would be close to the Northern Line tunnels beneath the river, and whilst they were perfectly confident that the piling contractor would be competent enough not to drop a concrete pile through one of the running tunnels, they weren’t confident that there was no UXO down there. Nothing had been recorded, certainly, but the thought of a pile being driven straight into an unexploded bomb, causing an underwater explosion that might then rupture the running tunnels, was just too horrible to contemplate. The design of the bridge was altered (at some cost) shortly after.

One London transport project though, more than any other in recent times, has involved being aware of (and looking for) UXO – Crossrail.

Crossrail’s Awkward Path

The reasons for this are simple. The Crossrail project involves construction and excavation on a scale unseen in London for a long, long time. To major station works at Liverpool Street, Farringdon, Tottenham Court Road and Bond Street must be added work on the tunnelling portals from which the running tunnels will be bored and the depots and line enhancements elsewhere. Perhaps more critically, Crossrail (like the Olympics) involves a huge amount of work in East London. It was the East, home both to various heavy industries and to the docks so vital to Britain’s war effort, that suffered most during the Blitz. Using the unmistakeable outline of the River Thames as a marker, the Luftwaffe made East London – and the docks more specifically – the most heavily bombed civilian target in the whole of Britain. There’s a reason that the streets of Hackney, Tower Hamlets, Newham and more have a thoroughly post-war look about them – it’s because whole swathes of those boroughs were bombed to the ground.

A Heinkel 111 Over Wapping

For Crossrail, this meant that from the very beginning the issue of UXO had to be at the forefront of their planning, one of the results of which has been a seven year relationship with special risk consultants 6 Alpha Associates.

6 Alpha are one of those discrete, and decidedly niche, firms that exist largely outside of public consciousness. In this instance that niche includes a great deal of expertise in the fields of UXO and EOD (Explosive Ordnance Disposal). On the Crossrail project, this meant a role in the early ground preparatory works – more specifically, a complete UXO survey for the length of the entire line.

“Sadly it’s not as glamorous a process as it sounds,” explains Lee Gooderham, the head of Alpha 6’s Explosive Remnants of War Section, “mostly its about collating documents from various archives and we’re lucky in London because the civil authorities – particularly the Port of London Authority – kept incredibly detailed records.”

It’s these records that form the basis of the UXO surveys and risk assessments that now underpin the Crossrail project. Indeed the scale and detail of this survey work has resulted in the creation of the first real industry-wide guidelines for the construction industry on how to plan for and deal with the issue of UXO. The combined efforts of the ARP wardens, Fire Watchers, the Observer Corps and other civilian volunteers have left modern engineers with a meticulous and reasonably accurate idea as to where bombs were dropped on specific nights. When combined with disposal records, these help paint a picture as to where any large-scale UXO might be, meaning that more detailed geophysical ground surveys can be targeted on the areas where the risk makes it warranted.

Much of this basic survey work has now been completed, but if you know where to look (and what to look for) you can still see some of the more detailed geophysical survey work taking place – particularly in areas where the current plans for Crossrail have changed from what they were seven years ago.

Right now, for example, this is most evident in and around Silvertown – because Crossrail’s plans with regards to the Connaught Tunnel have recently changed.

A Return to the Connaught Tunnel

We last visited the Connaught Tunnel in September 2010. First constructed in 1878 to take trains beneath the Victoria and Albert docks, the tunnel had lain disused since the North London Line connection to North Woolwich was permanently closed in 2006. As the photos that you can find here show, after years of closure the tunnel had become the epitome of an “abandoned line” – a pitch-black subterranean passage filled with fractured track, torn-up sleepers and a ground surface that one squelched through rather than walked upon. The tunnel was, however, intended to be a crucial part of the Crossrail project. Just as the Thames Tunnel (Marc Brunel’s largely forgotten masterpiece of engineering) still forms a crucial part of the London Overground, it was decided that the Connaught Tunnel would play a similar role for Crossrail.

The tunnel today is a very different place from what it was a year ago. Vinci won the contract to renew it, and work has been underway to clear, clean and renew the tunnel. As can be seen from the photos below, the majority of the tunnel has now been cleared, and work is underway to remove the ballast, lower the tunnel floor (so that the Tunnel is large enough to carry the OLE) and renew the drainage.

The Tunnel, Looking South

Work Continues In The Tunnel

Looking North Out Of The Tunnel

More extensive geophysical surveys carried out as the renewal project has advanced have, however, raised questions as to whether the point where the tunnel passes closest to the passage that links the Victoria and Albert docks is as strong as it needs to be. This was a known risk – the dock bed was lowered in the thirties in order to allow larger ships to enter. So much so that several instances of ships scraping across the top of the tunnel were recorded and iron rings were added inside to reinforce it.

The Channel Connecting the Docks

The plan had been to remove these rings, backfill the tunnels with concrete and then effectively bore new tunnels through that, but as Linda Miller, the Tunnel’s Project Manager explains, two factors now make this impractical. Firstly the tunnel’s roof is even closer to the surface than was thought – to the point where divers investigating the site were able to feel the brickwork through the mud at various points. Secondly, has been the appearance of something that those tunnelling beneath the Capital fear almost as much as UXO – unexpected tunnels.

In Connaught’s case, these are three smaller service tunnels that now appear to run alongside the main tunnel. The first hints that these might exist came from an 1878 schematic of the tunnel. The specific purpose of these and their original relationship with the Connaught Tunnel itself remains unknown, but geophysical surveys of the dock bed have established conclusively that they exist and that – worse – the lowering of the dock led to them being breached from above.

An 1878 Diagram of the Tunnel

The 1878 Cross Section

Both of these factors mean that if the iron rings were removed, there is no guarantee that the tunnel could stand up to the pressure of the water from above and its sides long enough for the backfilling to take place. Instead this section of tunnel will now be reconstructed in the same way that it was built in the first place – a cofferdam will be put in place and the tunnel will be rebuilt using cut and cover.

An Overview of the Work, Courtesy Gregor the Engineer

Reassessing the area

It is this that has resulted in the renewed need for detailed UXO work. The Connaught Tunnel itself bears the scars of a direct hit suffered in 1940 and the archival surveys suggest there are potentially five or more elements of UXO in the area.

The concrete plug for the 1940 bomb damage. This was clearly put in place over three days. Ahead of a comprehensive survey, friendly debate currently rages amongst the engineers as to its likely quality.

As a result, the area now plays host to a Fugro survey van, from which more detailed magnetic surveys can be carried out. From here, the ground can be probed at regular intervals and possible UXO discovered, investigated and dealt with by an EOD team if necessary.

The Survey Truck In Action

The Ground Probe Inside the Truck

UXO is a small world – it emerged that Lee Gooderham and on-site EOD man David Bird had previously worked together clearing ordnance after the Iran-Iraq war.

As can be seen above, it’s a relatively nondescript van for a rather serious purpose. Another subtle reminder of the London’s part in the Second World War. As the construction of Crossrail continues, and with other projects such as HS2 lurking on the horizon, more UXO work will likely be needed in the Capital. Hopefully it will continue to yield little in the way of physical results, but as those Olympic workers discovered in 2008, it’s still best to check, just in case…