What is Unexploded Ordnance (UXO)

A ‘High Explosive’ (HE) material is one that is designed to detonate (as opposed to deflagrating or ‘Low’ explosive). It is characterised by extremely rapid decomposition and development of very high pressure. When such explosive is encased, it effectively becomes a ‘bomb’.

During WWII, conventional high explosive bombs were dropped in their thousands by both German and Allied forces. They had a thick metal casing that would fragment on detonation. The main charge would be triggered by a fuze. In terms of weight of ordnance dropped, HE bombs were the most frequently deployed by the Luftwaffe during the war.

Common variants of high explosive bombs dropped on the UK during WWII were the 50kg, 250kg and 500kg – with a smaller percentage of 1000kg (nicknamed the ‘Hermann’) and 1800kg (the ‘Satan’).

Although efforts were made to identify the presence of unexploded ordnance following an air raid, often the damage and destruction caused by detonated bombs made observation of UXB entry holes impossible. The entry hole of an unexploded bomb can be as little as 20cm in diameter and was easily overlooked in certain ground conditions.

Incendiary bombs (IBs) are air-delivered weapons designed to cause fire. During WWII, there were several variants utilised by the Luftwaffe – from the small 1kg IBs to large oil/phosphorous bombs.

In terms of the number of weapons dropped, small IBs were the most numerous. Hundreds of thousands of these were dropped throughout WWII. The 1kg variant was magnesium cased and filled with thermite. They were dropped in containers, which would release the bombs at height, often distributing them over a wide area. When they failed to explode, they could easily go overlooked within debris/rubble, or in certain ground conditions.

Large incendiary bombs were often the same shape as HE bombs. However, they were thin-skinned and were not designed to penetrate the ground, but to split and spread their contents.

Also referred to as ‘Aerial Mines’ or ‘Ground Mines’, German Parachute Mines were an adapted naval weapon which were deployed over land targets to act as large blast bombs. They were very large weapons, designed to have slow rate of descent on a parachute enclosed within the body of the device. They were first used against land targets in the UK in September 1940. The two main variants were the Luftmine A (LMA), weighing 500kg, and Luftmine B (LMB) totalling 1,000kg.

When these mines were utilised against targets at sea (their original purpose), they would sink to the bottom, and an anti-shipping detonator would activate. These were originally magnetic, but later both acoustic and magnetic/acoustic fuzes were used.

Whilst it would not be expected to commonly encounter these on land, they are frequently encountered in the marine environment, and should be considered during offshore works.

A grenade is a short range weapon designed to kill or injure people. It can be hand thrown or fired from a rifle or a grenade launcher. Grenades can contain high explosive or smoke producing pyrotechnic compounds. Some common variants have a classic ‘pineapple’ shape (such as the No. 36 grenade, in service from 1915 until the 1980s).

A modern hand grenade generally consists of an explosive charge, a detonator mechanism, an internal striker to trigger the detonator, and a safety lever secured by a pin. The user pulls the safety pin before throwing, and once thrown the safety lever gets released, allowing the striker to trigger a primer that ignites a fuze, which burns down to the detonator and explodes the main charge.

A mortar is a generally simple, portable, lightweight, muzzle loaded weapon, consisting of a metal tube on a baseplate which launches mortar rounds in high-arcing ballistic trajectories. The mortar round is normally nose-fused and fitted with its own propelling charge. Its flight is stabilised by the use of a fin.

They are usually tear-drop shaped (though older variants are parallel sided), with a finned ‘spigot tube’ screwed or welded to the rear end of the body which houses the propellant charge. Mortars are either High Explosive or Carrier (i.e. smoke, incendiary, or pyrotechnic).

A projectile (sometimes referred to as a ‘shell’) is propelled by force, normally from a gun, and continues in motion using its kinetic energy. The gun a projectile is fired from usually determines its size. A projectile contains a fuzing mechanism and a filling. Projectiles can be high explosive, carrier or Shot (a solid projectile).

The most common type of ordnance encountered on land used by the military are items of Small Arms Ammunition (SAA). SAA refers to the complete round or cartridge designed to be discharged from varying sized hand-held weapons such as rifles, machine guns and pistols.

SAA can include bullets, cartridge cases and primers/caps.