Unexploded ordnance (UXO) is not the first thing most archaeologists expect to encounter when opening a trench, yet discoveries of historic munitions occur with surprising regularity across the UK. From rural training areas to former industrial centres, the legacy of 20th‑century conflict lies hidden beneath the ground—sometimes directly within areas of archaeological interest. Understanding why UXO appears on digs, how to respond safely, and when formal risk assessments are required is essential for responsible excavation practice.
Why Archaeologists Encounter UXO
Archaeological excavations often take place in locations with long, complex histories of land use. Many of these sites were active during the First and Second World Wars (WWI/WWII), even if no visible evidence remains today. UXO may be encountered because:
• Historic military activity overlapped with earlier settlement patterns. Hillforts, open fields, and coastal areas—prime archaeological landscapes—were also used for training, defence, or weapons testing.
• Urban bombing during WWII affected many historic towns. Post‑bombing clearance was often incomplete, leaving unexploded bombs or smaller ordnance buried beneath later redevelopment layers.
• Agricultural land was repurposed during wartime. Fields used for centuries of farming or habitation were temporarily converted into training grounds, airfields, or defensive positions.
• Post‑war disposal practices were inconsistent. Surplus munitions were sometimes buried, burned, or abandoned, particularly in remote or rural areas.
Because archaeologists routinely excavate deeper and more systematically than most construction activities, they are often the first to uncover ordnance that has remained undisturbed for decades.
Training Areas and Wartime Sites
Large areas of the UK were used intensively for military training during both world wars and the Cold War. These include:
• Infantry and artillery training grounds in places such as Salisbury Plain, Thetford Forest, and parts of North Yorkshire.
• Airfields and bombing ranges, many of which were rapidly constructed and later abandoned.
• Coastal defence zones, where live‑fire exercises and anti‑invasion preparations were common.
• Home Guard training sites, often informal and poorly documented.
Even small, localised training areas—rifle ranges, grenade pits, or mock assault courses—can leave behind hazardous remnants. Archaeological projects in these landscapes frequently uncover:
• Live or practice mortar rounds
• Artillery shells
• Small‑calibre ammunition
• Grenades and pyrotechnics
• Fuzes, detonators, and other explosive components
CIRIA C681 highlights that former training areas present some of the highest likelihoods of encountering UXO, particularly where records are incomplete or where land has reverted to agricultural or recreational use.
Small Arms and Grenades Found on Digs
The most common UXO encountered by archaeologists tends to be small items, often mistaken for scrap metal or harmless debris. These include:
Small Arms Ammunition
• Rifle and pistol rounds
• Blank cartridges
• Buried ammunition boxes or dumps
Although small, these items can remain hazardous—especially if corroded, deformed, or containing propellant.
Hand Grenades
Archaeologists frequently uncover:
• Mills bombs (No. 36 grenades)
• Smoke or phosphorus grenades
• Practice grenades with partial explosive content
Grenades are particularly dangerous because deterioration can make them unstable, and their appearance is often disguised by corrosion or soil accretion.
Mortar and Projectile Rounds
Even small‑calibre mortars can contain significant explosive charge. These are sometimes found on rural digs, especially near former training grounds.
The key challenge is recognition. Many items resemble stones, metal fragments, or harmless artefacts. This is why awareness and appropriate procedures are essential.
Procedures When Ordnance Is Discovered
CIRIA C681 provides clear guidance on what to do when suspected UXO is encountered. Archaeologists should follow a simple, disciplined process:
1. Stop Work Immediately
Cease all excavation in the immediate area. Do not touch, clean, or move the object.
2. Establish a Safe Exclusion Zone
A minimum cordon of 5–10 metres is typical for small items like rounds, but this be expanded to a minimum of 100 metres for all other items.
3. Notify the Site Supervisor
The discovery should be escalated through the project’s established reporting chain.
A qualified UXO engineer can identify the item, assess the risk, and advise on next steps. In many cases, they can confirm whether the item is inert or requires police/EOD attendance.
5. Follow Emergency Services Guidance
If the item is confirmed as live, the police will coordinate with Explosive Ordnance Disposal (EOD) teams to remove or destroy it safely.
6. Record and Report
The find should be documented in the site records, including:
• Location
• Depth
• Description
• Photographs (taken from a safe distance)
This information helps refine future risk assessments and contributes to the archaeological record.
When UXO Risk Assessments Are Required
Under CIRIA C681, a UXO risk assessment is recommended whenever ground‑intrusive work is planned in an area with potential for historic military activity. For archaeological projects, this includes:
• Sites within or near former training areas, airfields, or wartime infrastructure
• Urban excavations in cities heavily bombed during WWII
• Rural landscapes with documented Home Guard or auxiliary unit activity
• Locations with known disposal pits or post‑war dumping
• Any site where previous UXO discoveries have been recorded
A Preliminary UXO Risk Assessment (PRA) is typically the first step. If elevated risk is identified, a Detailed Risk Assessment (DRA) and UXO Risk Mitigation Plan may be required. These assessments help archaeologists plan safe excavation strategies, brief staff appropriately, and ensure compliance with health and safety legislation.
Conclusion
UXO is an often‑overlooked but very real hazard during archaeological excavations in the UK. By understanding the historical context, recognising common ordnance types, and following CIRIA C681 procedures, archaeologists can manage the risk effectively without compromising the integrity of their work. As the UK continues to explore its rich past, awareness of wartime legacies remains essential for safe and responsible archaeology.
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