BOMBS

Between 60-70,000 tonnes of bombs were dropped across the United Kingdom during WW2, with over 60,000 people being killed by the bombing raids.  In a single night in April 1941, some 446 tonnes of bombs were dropped on London.          with around 58 tonnes not exploding.

A 1942 photo showing five high explosive bombs, with two female adults to provide the scale:
50kg (front, second from left) 250kg (front, centre) 500kg (left) 1800kg, known as "Satan" (rear, black) 2500kg known as "Max" (right)

Several different types of bombs were dropped by the Luftwaffe on the United Kingdom, 

• High explosive general purpose blast bombs, ranging from 50kg to 2500kg (Sprengbombe Cylindrich/SC bombs).
• High explosive armour/reinforced concrete penetrating bombs, ranging from 50kg to 1700kg (Sprengbombe Dickwandig/SD and Panzerbombe Cylindrich/PC bombs).
• High explosive sea mines, used on land with the aid of a parachute, usually weighing 500kg or 1000kg (luftmines).
• High explosive anti-personnel blast bombs, usually weighing 2kg Butterfly Bombs(SD2).
• large incendiary oil bombs, either 250kg or 500kg (Flammenbombe).
• small incendiary bombs, usually 1kg or 2kg, dropped in containers holding many sub-munitions.

         There were three main reasons why these WW2 bombs did not explode:

• Damage to the bomb breaking up on impact, or premature destruction of the fuzes
• Technical failure, sometimes due to sabotage by the slave labour used in factories
• Designed by the Germans, so they would cause disruption, fear and casualties when discovered or handled​

It is estimated that over 10% of the high explosive bombs dropped across the United Kingdom failed to explode, with many of them are still to be found.

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